Remove workaround for persistent errors

Allow installing on Dev16.
Allow to specify rootSuffix.
Bump min required VS version to 15.8.
Misc cleanup.

Merge pull request #32649 from jasonmalinowski/fix-metadata-references-not-always-having-file-watchers

Fix metadata references not always having file watchers

Gracefully handle documented exceptions from AssemblyMetadata.GetModules

Remove additive classifications when generating ClassifiedText from ClassifiedSpans

 Add structure provider for interpolated strings

Tweak bail out approach from unused member analyzer for struct layout types

Issue 27925 - Squiggle first line / entire parenthetical expression in remove unnecessary parentheses diagnostic (#32500)

* Update unnecessary parentheses analyzer to squiggle the entire
expression / first line.
Resolves #27925 

Fix cast exception in AbstractProject.RemoveDocument

Many of these can be called fairly often, so this avoids allocations in
the common case we don't refresh anything.

this is so that we don't get this kind of issue (https://github.com/dotnet/roslyn/issues/31928) by throwing argument exception invalid argument is given

Fix preview changes application for linked files

We have done so in past for other callsites to this API, such as #17687. This change does the same for the remaining two callsites in the IDE layer.

Fixes VSO Watson [234447](https://devdiv.visualstudio.com/DevDiv/_queries/edit/234447): [Watson] clr20r3: CLR_EXCEPTION_System.BadImageFormatException_8007000b_Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.PEModule.get_ReferencedAssemblies

Fixes #32216

* Remove obsolete comment.
Fixes #32315

* Add additional verifications in tests for recursive patterns.
Related to an issue in https://github.com/dotnet/roslyn/issues/32012

Dispose pattern based enumerators in foreach

AbstractProject.RemoveDocument was trying to support removing
ContainedDocuments, but had a misplaced cast which negated the whole
attempt.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/776782

Enable Mono testing

2 new options. NullableContextOptions and MetadataImportOptions

if compiler team do this (https://github.com/dotnet/roslyn/issues/12795), IDE side can simply use compiler's serialization rather than doing it in IDE side

Current implementation bailed out in symbol start action, which caused both analysis and reporting to be skipped for unused members in a type with StructLayout attribute. New implementation bails out in symbol end action, so we only skip reporting not analysis.

Fixes #32727

Update the Spanish_Unit_Tests test results path

https://github.com/mono/mono/issues/12603

These issues should be fixed now. Enabling the assemblise again.

Fixes https://github.com/dotnet/roslyn/issues/20118

Sign SCI and SRM with Windows 10S compatible certificate.

Handled exception from a COM call to `IOleUndoManager`

Fixes #32490

When showing the preview changes dialog, we correctly de-duplicate the linked files by only showing changes for a single file. When applying changes, we undo changes which have been unchecked by the user in the preview changes dialog. However, the latter did not account for linked files. This led to us undoing unchecked changes for non-linked files, but not for linked files. This PR ensures that we also handle linked files when undoing changes.

- Add verifyIL to a ref struct test to ensure we don't box