Breaks the internal GTD infrastructure into seperate symbols for
determining the navigable symbol at the caret position and performing
the navigation.

this is port of https://github.com/dotnet/roslyn/pull/20968 to dev15.3.x

code

If you create an elision buffer, there's no way to disconnect the
elision buffer from the underlying buffer once you're done with it,
causing the elision buffer to leak. It's possible to disconnect
projection buffers, so we use them to work around this limitation.

When we create a projection buffer, that buffer is strongly held by
the underlying buffer, which means we have a memory leak unless we
disconnect it by unmapping all spans. This also causes problems because
bugs in the editor around projections can then cause crashes when we
didn't actually need the buffers anymore.

Revert "Merge pull request #20558 from Pilchie/Fix19968-DuplicateSourceAndAdditionalFiles-DistinctIds"

This reverts commit 6f5b2d47, reversing
changes made to 66362df5.

If the user closes a textview while completion is filtering, it's possible for the filtering task to ask for a Document before it gets cancelled, resulting in a crash. To prevent this, restrict Controller.GetDocument() to the foreground thread.

This is a breaking API change.  Need to decide if we want to take it or
not.

We previously assumed that conditional element access would never be followed by a member or conditional access.

Fixes https://github.com/dotnet/roslyn/issues/20507

Clear completion pattern matcher caches on solution close

made diagnostic engine to verify span given to diagnostic from analyzers. and added explicit check in tagger for out of range

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.

Refactor tests

Add a unit test to ensure that analyzer execution does not leak solution instances from preview workspace.

One path in the VB type inferrer assumed that invocations of Select() would always have an argument list, leading to crashes. We now check that it is not null before accessing it. This is the only unguarded use of this property in the type inferrer.
Fixes  https://devdiv.visualstudio.com/DevDiv/_workitems?id=431509&_a=edit&triage=true

Add option to disable OOP diagnostics during testing.  They don't currently work with the CodeAction testing infrastructure.

We believe that the primary cause of this exception (some issues around
projection buffers) was worked around in d8f8dad3 but we're still
seeing issues so that's not the case. I'm also further not convinced
that change helped at all, because in many case we already fork
buffers to work around the same issue.

It used to switch on Tag type to determine which tagger to use, now the tagger type is directly used as the type parameter.

We simply have to produce IErrorTag with with "hinted squiggle" type and the editor will make tooltips and the adornment "just work"