Merge Features/async main

tests only. no ask mode approval is required. thanks!

Use-throw-expression should not be offered when the 'if-block' has additional statements in it

Pool the simplifiers we use when simplifying code.

Preserve trivia when converting a numeric literal base

* remove remaining prototype comments, add extension method tests

* fix old test, address review feedback

* ReturnType implemented on each subclass

* added more tests on non-async task returning mains

* add obsolete tests

* autoformat

* add better tests for successful task overrides

Fixes #19280

Re-enable roslyn analyzers on Roslyn.sln and update public api file f…

Tests only. No ask mode approval is required.

Refactored IErrorReportingService

Simplify serialization.

Re-enable roslyn analyzers on Roslyn.sln and update public api file for an IOperation API change merged yesterday (#19278).

Revert "Merge pull request #10993 from rchande/quickinfosession"

Fix analysis of IOperation descendants for BoundDelegateCreationExpre…

* simplify partial method return type syntax finder tests

* Bug fixes and API use changes

* address first review

* better comment and compiler trait on class

* fix tests, pull entrypoint check out into local function

* unify diagnostics for intvoid or task mains

* add more tests, change error text

* address review

* finish tests

* be explicit on language version in tests

* add another test, fix typo, add diagnostics even when they aren't likely to exist

* rewrite error->warning code, add more cases to tests

* change test language versions

* formatting on comments and adding WithLocation to tests

* fix formatting for some tests

* fix some formatting and added withlocation

* fix withlocation

Allow the Simplify Type Names analyzer to run concurrently