Check local symbols to ensure that suggested name is appropriate, otherwise append a numerical suffix.

Resolves #31304 

These can be very confusing, since other methods on Contract actually
throw exceptions. Since we have endless amounts of code directly calling
Debug.Assert, let's just use it everywhere.

Also add
- CommonConversion.IsImplicit
- Compilation.HasImplicitConversion
Fixes #9461

* foreach to for for C#

* use different method

* no ctor needed

* initial vb support

* added more tests in vb, more code share. more trivia tweak on vb

* more referrence cases

* handle embeded statement case

* some clean up

* addressing some feedbacks. some clean up and etc

* added more unit tests, more refactorings

* assigning better collection name

* more refactoring

* added comment

* more feedback updates

* removed old resource

* use semanticFacts.GenerateUniequeName

* changed to use TypeStypleHelper

* added style test

* fixed test failure

* fix up resx file.

* improve local variable name handling

* updated title.

removed from part.

* share duped code

* missed some places to convert to new dedup method

* more feedbacks

* fix up test failures due ot GenerateUniqueLocalName changes.

* Rename files.

* Initial support for GotoDefinition in LINQ query syntax.

* Fixed naming issues.

* Fixed failing tests.

* Added support for Cast<> in from clause. Removed support for degenerated select clause. Reverted changes causing regressions.

* Added support for tokens to distinguish which MethodSymbol to return for a SyntaxNode that binds to more than one method. This adds support for range variable types and orderby.

* Fixed regression. Suppressed quick-info for degenerated query expressions.

* Added quick info tests according to the proposal.

* Added test for GotoDefinition. Moved logic for degenerated clauses to deeper layer.

* Added GotoDefinition for let test.

* Added test for incomplete orderby clause

* Code refactorings (Review feedback).

* PR feedback (nits)

* PR feedback (code comments).

* Revert changes in compiler.

* Revert changes in compiler (2).

* Added test for single from clause with out cast.

* Removed call to GetLanguageService and ValueTuple.Create

* Unify to return default;

* Corrected ISyntaxFactsService.IsQueryKeyword for VB and C#

* Support property generation for in arguments

* Use refactored API

* formatting

.. checks identifier checks for rename type.

for VisualBasic.

Renames various "Begin" and "End" property names in Syntax API to match the rest of the API with block specific names like "CaseStatement" "EndClassStatement" etc (changeset 1400806)

Marks CSharpKind and VBKind extension methods as Obsolete and adds equivalent extension methods Kind for both languages.
Marks CSharpKind and VBKind instance methods on language specific syntax nodes Obsolete as well.
 (changeset 1389494)