The error message in our compilers MSBuild NuGet package claims to support MSBuild 14.0. The actual version we support is 15.0.

added an ability to keep session alive for OOP

Improve code actions that are offered when code looks generic.
Fixes #19575

Merge master to dev15.6

Fix build errors related to the use of UserOperationBooster

Use the new valid rename field tag id in integration tests

Fix crash in VB type inferrer

Accessibility for Inline Rename in the Editor

This reverts commit 2fba37a6.

By design, when data flow analyzes local functions it does so devoid of
surrounding context and records possibly unassigned variables rather
than reporting a diagnostic. Thus, all captured variables are expected
to be marked unassigned during data flow analysis without reporting a
diagnostic.

However, reporting a diagnostic is not the only side effect of running
data flow analysis. By calling virtual methods data flow analysis
informs derived types of unassigned variables. While the diagnostic is
suppressed and recorded, currently the virtual method is still called.
This has negative consequences for region analysis, which considers
these calls as indications of variables flowing out of the given
region, which may not be the case for local functions.

This PR changes data flow analysis to only call the ReportUnassigned
virtual method if not inside a local function, excluding local functions
from all unassignment reporting.

Fixes #17165, #18347

Fixes
https://devdiv.visualstudio.com/DevDiv/_workitems?id=391624&_a=edit

- Inline Rename fields now consist of a themeable/customizable
background, foreground, and border. The border is used in High Contrast.
- Resolved and Unresolved conflict borders can now be themed &
customized.
- Resolved and Unresolved conflict borders now have different dash
styles so they are distinct from each other and regular Inline Rename
fields. The Dashboard shows a key indicating which type of conflict
corresponds to which border dash style.

Merge master to dev15.6

Skip repl VSI tests

Log telemetry if we see ITextBufferEdit.Apply() throwing exceptions

Failure tracked by https://github.com/dotnet/roslyn/issues/20219

Looks like there is still fall out from the licensing issue.  VS integration tests still failing
at 100% due to a timeout issue.  Change them to not run by default while we look into this.

Can still be run manually for testing with

test vsintegration please

Move language settings after SDK import

The new SDK unconditionally sets a number of MSBulid properties
including many that we depend on in Roslyn.  This is a break from the
old MSBuild behavior which respected initial values.

https://github.com/dotnet/sdk/issues/752

The behavior in 2.0 is changing to go back to the old model of
respecting initial values.  Roslyn though continues to often use the SDK
installed with Visual Studio.  That can be a variety of values from 2.0
prebuilds, to various drops of 1.0.

As a result the success / failure of our build can depend a lot on which
version of VS is installed and by consequence which new SDK comes with
it.  Subtle differences in the SDK can change the values we end up
compiling with in our project.  We've been guarding against this
by directly re-setting values we knew to be overidden in some version
of the SDK.

Now though I'm worried this isn't an adequete solution for the following
reasons.

- Just this week I got new warnings in the build by using a new VS
- The Microbuild lab is aggressively grabbing new builds of VS which
means the VS SDK is also potentially changing.

After some thought I decided to simply move all of our langauge specific
settings after we import the core targets.  Given that we
unconditionally set the values it becomes irrelevant what the SDK does
or does not respect.

Allocate less while performing classification.

Improve 'Initialize Parameter' so it works with members that don't have their bodies written yet.
Fixes #19956

Be resilient to running with System.IEquatable can not be found.
Fixes #20158

Fix race with boosting OOP priority.  Also, ensure FindRef calls are boosted.

Add SyntaxGenerator support for Tuples.

Merge master to dev15.6