Fixing a crash in SuppressDefaultTupleElements

* Enable finding the breakpoint location for a pattern switch case (#14426)
Fixes #12378
* Tests for IDE breakpoints for deconstruction foreach statement
Fixes #14439
* Implement and test sequence and break points for deconstruction foreach
Fixes #14439
* Implement and test sequence and break points for expression-bodied ctor, dtor, and accessors
Fixes #14438
* Enable setting a breakpoint in a local function
Fixes #14437
* Add support for /instrument codecoverage for new language features
Fixes #14337

We were missing a null check fo the container. In broken code it can be null.
Fixes: #14546

Disable Roslyn EnC handler for non-Roslyn languages

Propagate delegate relaxation information for tuple conversions.

Fix for XAML Dev15 RC issue #14565.

require 4.6.1 to be installed

Fixes #14255.
Also fixes #14530.

Fix some inconsistencies in our project files

These changes don't matter for command line builds, but the project
system interprets empty property groups to define which configuration/
platform combinations exist. Thus, those should line up with the intent
of the project. If there was ambiguity, I've resolved in favor of the
project.json statement of the world since that's what was actually
happening.

Merge pull request #14537 from heejaechang/fixNullException

Porting two recent tuple-related fixes to VB

Fixed null exception for solution which has both C#/VB and typescript/javascript

Fix several crashes in DPL/Lightweight solution load.

Fixes internal bug 268059.

In some cases (for example internal issue 273128, which is now fixed,
where the index would be return stale data if a solution was moved on disk),
we get project paths that aren't part of the solution and don't exist on disk.

Be resilient to this happening, even though we will end up trying to parse files
from their old locations, and won't recognize files from their actual locations.

Fixes internal issue 273134

Also, use PathUtilities consistently.

Fixes internal bug 272652.

If the indexing service fails to determine the commmand line arguments (for example because the
targeting pack is not installed), it passes us an empty string for the TargetPath.  Our code wasn't
prepared to handle an empty string, so convert it to null instead, which we are prepared to handle.

Fixes internal bugs 269571 and 274711.

This PR fixes speculative-T completion for the return type of local
functions. However, it doesn't include completion for generic arguments
to async local functions, which will require a significant change in the
parsing strategy and tree produced.

Fixes #13480.

Create an ExecutableCodeBinder when speculatively binding an expression or attribute.
Fixes #14384

porting 3 PR to dev15-rc - sharing checksum and enabling oop by default

the way we added cancellation support to StreamJsonRpc can cause ObjectDisposedException from happening.

Propagate InvolvesNarrowingFromNumericConstant flag for tuple conversions.

enable remost host by default

separated checksum creation from ISolutionSynchronizationService

Fix issue where we overly aggressively removed xml doc comment trivia.

Fixes #13436

Related to #14255.
Fixes #14473.