Merge dev15.6.x to dev15.7.x

This is necessary to install pre-release .debs of the Mono runtime.

Merge dev15.5.x to dev15.6.x

Do not do analysis for invalid argument escape mixing when having binding errors.

Lightbulb header accessibility when selected/focused

Choosing dev15.5.x as the base instead.

Choosing dev15.5.x as the base instead.

Add satellite assemblies to Microsoft.NETCore.Compilers

Merge dev15.6.x to dev15.7.x

This also lets the colors change appropriately when the theme is
changed.

Port fix for duplicate IDEDiagnosticIDs to 15.7

* Fix `is` and pattern-matching behavior in presence of implicit UD conversion
and also an explicit reference conversion. User-defined conversions should
never be considered for `is` and pattern-matching.
Fixes #24522

Merge dev15.6.x to dev15.7.x

Locate implementations for reference assemblies using the GAC

Update optimization data to 2.7.0-beta3-62526-01...

Fix command line build error

* Check fully-qualified names for SuppressIldasmAttribute and ReferenceAssemblyAttribute
* Use correct reference location, or fail decompilation if it's not available

Reduce allocations in UnboundLambda

Move to xunit.console for CoreClr tests

Verify MSBuild version in Developer CMD prompt

Fix and re-enable test that would catch this error