The synthesized constructor assigns the properties, if they are
synthesized properties. The properties are synthesized only if no
conflicting member already exists in the class.

Capturing lambdas should be avoided in core compiler code
as they generate excess allocations

Fixes #41054

* Insert correct `WithNullableContext` binder into the binder chain to ensure speculative models return correct information based on speuclation location.

* Refactor Nullable context options to rely on an enum instead of two bools.
Break out the BuckStopsHereBinder's code to allow sharing.
Fix binder ordering issue for TryGetSpeculativeSemanticModelForMethodBody.

* Make NullableContextState.State a byte for space.

Addresses 3200MB allocations while analyzing Roslyn.sln.

Addresses 950MB allocations while analyzing Roslyn.sln.

Addresses 950MB allocations while analyzing Roslyn.sln.

Addresses 2400MB allocations while analyzing Roslyn.sln.

This just adds a synthesized symbol (no body) for the constructor.

Preliminary spec work at https://github.com/dotnet/csharplang/pull/3076

Addresses 815MB allocations analyzing Roslyn.sln.

Addresses 680MB allocations analyzing Roslyn.sln.

The `SyntaxNodeOrToken` type had four states:

1. It's a `SyntaxNode`
1. It's a `SyntaxToken`
1. It's `default(SyntaxNodeOrToken)`
1. It returns `true` for `IsNode` but `AsNode` returns `null`

The fourth state appears to be an accident of implementation. This
change removes that state. The one place in the code where this appeared
to be an issue is in the implicit conversion from `SyntaxNode?` to
`SyntaxNodeOrToken`. In all places where this was used and the value was
potentially `null` the caller only used `GetLocation` on the result.
Hence the fix is simply to change that API to return `default` instead
of the fourth state in the case of `null`

1. Make the strings sentence cased
2. Rename "Open Documents And Projects" to "Open documents" as per internal review.

This is not a user facing string, so must not be localized. Additionally, with https://github.com/dotnet/roslyn/pull/38886, we now support bulk severity configuration in editorconfig based on diagnostic category, so the string ought to be a non-localized constant without any spaces.

Fixes #40917

Address feedback from https://github.com/dotnet/roslyn/pull/40900

Update src/Features/Core/Portable/RemoveUnusedParametersAndValues/AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.SymbolStartAnalyzer.BlockAnalyzer.cs