Use ScriptCompilationInfo.ReturnTypeOpt instead of ReturnType when
chaining off a previous compilation to ensure that the derived
ScriptCompilationInfo has the same ReturnType.

Fixes #10023.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=233669.

Fixes #14365.

Merging on behalf of @alrz. Thanks for the contribution.

Provide an API to get unreferenced assembly identities obects from the diagnostics reported about them.

Use tuple syntax in the compiler

Support setting if an anonymous type's properties are mutable or not.

This change drops support for .NET 4.5 and retargets to desktop
4.6 + CoreCLR. It also fixes up various analyzer warnings that
were created due to the move.

Fixes #12926

* CommonPEModuleBuilder refactoring

* Renames

* Use CommonPEModuleBuilder instead of IModule

* Remove IModule

* Move GetFiles to module builder

* Remove IAssembly

* Add comments, PR feedback

* Resolve merge conflicts

and SpecifiedLanguageVersion to the parse options.

* Implement source link feature

* Fix CommonCompiler to open source link stream, add E2E tests

* Reduce code duplication across VB and C#

Revert "Revert "Revert "Revert "*DON'T MERGE INTO MASTER* Hide IOperation API behind a feature flag""""

This reverts commit d4d502e4.

[Based on features/async-return with tests ported from that branch.]

For the most part, this change implements the same encoding
for tuples that we use for dynamic. This means that interface
implementations and generic constraints are not covered, but
base types and type parameters are.

This change also doesn't have full tests for "long" tuples (nested tuple
transformations) or tuple types that can only be constructed in
metadata.

- Substitute underlying type with corresponding tuple type at the point of type reference.
- Adjusted implementation of symbol display to account for presence of names in the extension tuples.
- Implemented proper retargeting for tuple types (multi-targeting support).

- Include memebers of underlying type into a set of members returned by
tuple type symbol. Properties and events are not supported at the moment.
- Track declaration locations for tuple related symbols.
- Ensure Rest extensions are tuples.

Ensure that we generated a CompilationCompletedEvent for compilations with no source files (example an empty VSIX projects).

Ensure that we generated a CompilationCompletedEvent for compilations with no source files (example an empty VSIX projects).

This reverts commit a96d7825.

This reverts commit 92ff3f8d.