Closes #30171.
Closes #29838.

* Source changes for unmanaged (PROTOTYPE for metadata)

* Modreqs for unmanaged as well

* Finished roundtripping metadata

* Added more tests

* Fix CI

* More tests

* Clean up

* Marshalling methods with `in` parameters should have [In] attribute

* Apply [In] on all `in` parameters

* More tests

* nit

* In parameters cannot have Out attributes

* PR feedback

* Follow up

Merged on behalf of @svick. Thanks for the contribution!

LocalFunctionTypeParameterSymbol isn't necessary as long as the functionality around type constraints can be moved into a shared base class between ordinary method symbols and local function symbols.
In fact, it would be very useful to have a shared base symbol aside from MethodSymbol between local functions, lambdas, and other source method symbols. To this end, I've renamed SourceMemberMethodSymbol to SourceOrdinaryMethodSymbol (since it is just used for ordinary member-level methods), SourceMethodSymbol to SourceMemberMethodSymbol (since it is only used as a base class for member-level method-like functions like ordinary methods, constructors, property accessors, et al.), and added a new abstract class SourceMethodSymbol that is the root of both LocalFunctionSymbol and SourceMemberMethodSymbol. This lets us unify all source method-like symbols under a single base class, SourceMethodSymbol.
The first three commits perform the refactoring, while the last commit actually removes LocalFunctionTypeParameterSymbol and moves the necessary functionality into SourceMethodSymbol. I expect more functionality to be moved over in subsequent PRs.

Fixes #17244

* Call this.DeclaringCompilation.EnsureReadOnlyAttributeExists() when needed

* Promote EmbeddedAttribute to be used by both compilers

* Generate Embedded attributes on PE Module Builder

* Thread PEModuleBuilder through Symbol.AddSynthesizedAttributes()

* Fix failing tests

* Base case passing

* Refactor ReadOnlyAttribute to IsReadOnlyAttribute

* Fix build break

* More Tests

* Clean up

* PR Comments #1

PR Comments #3

PR Comments #4

PR Comments #5

PR Comments #6

PR Comments # 7

* Handle NoPIA

Added more tests

* Lambdas and Local functions no longer generate attributes in symbols

Added tests for constructors and operators

Signal need for synthesized attributes in local rewriter for lambdas an local functions

Clean up

* Clean up

* More PR Feedback

* Adding more tests

* More PR Comments

* More tests for explicit interface implementations

* Latest PR Comments

* Moved EnsureIsReadOnlyAttributeExists to AfterAddingTypeMembersChecks

* Fix failing tests

* Writing attribute to metadata

* Reading attribute in PE symbols

* Added more tests for lambdas, delegates, and other types

* Use ReadOnlyAttribute instead

* Fix build break

* Fix Failed Tests

* Enable back disabled tests

* Fix more tests

* Ban usage of ReadOnlyAttribute in source

* Rename System.Runtime.InteropServices.ReadOnlyAttribute to System.Runtime.CompilerServices.ReadOnlyAttribute

* Clean up

* Address CR comments

* More PR feedback

Make local function default parameter value binding lazy

Current strict binding can cause circularity problems when local
functions are referenced. This change causes local functions to use lazy
default parameter binding, similar to methods, and then forces their
construction when diagnostics are requested for the local function.

This also requires a mechanism for recording declaration diagnostics
outside of adding to the compilation's DeclarationDiagnostics. A new
type, DeclarationDiagnosticStore is introduced as an abstraction to
store declaration diagnostics on either the compilation or in a local
DiagnosticBag, depending on the needs of the symbol storing diagnostics.

Fixes #16451, #17293

Even for cases when the parameter is not part of a type member declaration, i.e. owned by an anonymous method or a local function.
Fixes #16748. Fixes #16374.

Also implement SemanticModel.GetDeclaredSymbol(ParameterSyntax) for parameters of a Local Function.
Fixes # 16757.

Fixes #16167

Internal APIs are aligned with these public APIs.
VB Symbol Display for ByRef returns is adjusted according to the latest design decision.

* Bug 217740: Repro and test harness for C#

* Testing and fixing loading scenario in C# and VB

* Verifying VB case using attribute on field

* Adding more tests

* Adding VB tests

* Adding tests

* More tests on fields with double-attributes

* New test constraint

* Fixing VB side to new test constraints

* Fixing C# side to new test constraints

* Fixing remaining tests

* Adding comments

* Fixing VB field scenario too

Add ability to associate annotations with type symbols exposed by other symbols. For example, with property's/method's return type, parameter's type, etc. As part of this change, custom modifiers are now handled as an annotation.

Fixes #4163.

SymbolEquivalenceComparer improvements: custom assembly comparer, handling custom modifiers, comparing method return types

Related to #846.

     Background:

     As discussed in the dev team all hands all code under the GitHub dotnet foundation is using a single process for contribution, API review, infrastructure and coding style. The idea is to present a unified view to our customer and give them a single story for contributing to any project under the dotnet foundation.

     https://github.com/dotnet/corefx/wiki/Contributing#c-coding-style

     The coding style transition is automated using a Roslyn based rewrite tool:

     https://github.com/dotnet/codeformatter

     This will be applied in stages across our developer tree. Right now the focus is on the Open directory as this is what is being presented on github. Code owners will be contacted before the transition happens.

     Note: this is a soft style requirement. There are no build errors that come from this change.
 (changeset 1408227)