Fix VB IConversionExpression bug.

* dotnet/features/ioperation: (151 commits)
  Fix VB labeled statement tests.
  Document compatibility issue with EmitOptions change (#21394)
  Remove 'ignoreTrivia' option from tests.
  Fix Test break due to missing ConfigureAwait
  Updated doc comment.
  EnC statement matching and editing for local functions (#21599)
  Fix unit test and compiler traits for a bunch of unit tests
  Add a missing ConfigureAwait call caught by analyzer
  Fix link.
  Don't include missing tokens when creating a breakpoint span.
  Address PR feedback and add more unit tests
  restore code.
  Add test.
  KeepAliveSession was handling same situation properly already. added test
  Be a bit paranoid before calling to get a compilation from a random project.
  Only try to get a compilation for a language that supports it.
  ported StreamRpc cancellation issue #21702
  Add fields as members of synthesized structs (#21649)
  Revert "Revert "Merge pull request #20592 from sharwell/fix-options-page""
  Keep TaskExtensions.cs changes
  ...

ILabelStatement Refactor

Refactor IConditionalAccessExpression

Refactor ILocalFunctionStatement.LocalFunctionSymbol to .Symbol, upda…

* dotnet/features/ioperation: (126 commits)
  Document compatibility issue with EmitOptions change (#21394)
  Remove 'ignoreTrivia' option from tests.
  Fix Test break due to missing ConfigureAwait
  EnC statement matching and editing for local functions (#21599)
  Fix unit test and compiler traits for a bunch of unit tests
  Add a missing ConfigureAwait call caught by analyzer
  Fix link.
  Don't include missing tokens when creating a breakpoint span.
  Address PR feedback and add more unit tests
  restore code.
  Add test.
  KeepAliveSession was handling same situation properly already. added test
  Be a bit paranoid before calling to get a compilation from a random project.
  Only try to get a compilation for a language that supports it.
  ported StreamRpc cancellation issue #21702
  Add fields as members of synthesized structs (#21649)
  Revert "Revert "Merge pull request #20592 from sharwell/fix-options-page""
  Keep TaskExtensions.cs changes
  Keep PreviewPaneService.cs
  Update ServiceHubRemoteHostClient.cs
  ...

Merge remote-tracking branch 'dotnet/features/ioperation' into refactor-iconditionalaccessexpression

* dotnet/features/ioperation: (145 commits)
  Document compatibility issue with EmitOptions change (#21394)
  Remove 'ignoreTrivia' option from tests.
  Fix Test break due to missing ConfigureAwait
  EnC statement matching and editing for local functions (#21599)
  Fix unit test and compiler traits for a bunch of unit tests
  Add a missing ConfigureAwait call caught by analyzer
  Fix link.
  Don't include missing tokens when creating a breakpoint span.
  Address PR feedback and add more unit tests
  restore code.
  Add test.
  KeepAliveSession was handling same situation properly already. added test
  Be a bit paranoid before calling to get a compilation from a random project.
  Only try to get a compilation for a language that supports it.
  ported StreamRpc cancellation issue #21702
  Add fields as members of synthesized structs (#21649)
  Revert "Revert "Merge pull request #20592 from sharwell/fix-options-page""
  Keep TaskExtensions.cs changes
  Keep PreviewPaneService.cs
  Update ServiceHubRemoteHostClient.cs
  ...

Merge master to features/ioperation

Merge master to features/ioperation

Remove 'ignoreTrivia' option from tests.

IBinaryOperatorExpression, IUnaryOperatorExpression and IIncrementExp…

Avoid double-type-checks in CSharpSemanticModel

Don't include missing tokens when creating a breakpoint span.

Only try to get a compilation for a language that supports it.

Merge dev15.4.x to master

added test for StreamRpc cancellation issue #21702 for master

Merge master to features/ioperation

In order for EnC and other mechanisms to work we have to add synthesized
members to a list in the CommonPEModuleBuilder for a compilation (these
synthesized members are then queried as part of compilation stages).
If those members are struct fields, we don't add them to the struct
definition, only to the list of synthesized members. This works for
emit, since we explicitly emit everything in the synthesized list, but
it doesn't work for any compiler pass that examines the members of the
struct for semantically meaningful reasons.

This is the case for the CaptureWalker for async and iterator
expressions. The walker checks the members of structs when a field of a
struct is assigned to see if the struct has been assigned piecewise
(each of its members has been assigned individually). If so, it will
mark the entire struct as assigned. By not including synthesized fields
as proper members of the struct type, the assignment pass believes that
many fields have been assigned that have not, and thus marks the full
struct as assigned, leading to losing track of variables captured across
await/yield statements.

This PR fixes the problem by adding the fields to the
SynthesizedContainer, but exlcuding them from emit, since we should
continue to use the emit mechanism used for CommonPEModuleBuilder.

Fixes #21409

Pause OOP server when 'global operations' (i.e. build) are executing.