Fix #894: hover for locals, ctor params, and members inside init() bodies

[DavidObando]

Fixes #894

Problem

Hovering over a local variable, a constructor parameter, or a class member referenced inside an init(...) constructor body produced no hover result, while the identical reference inside a normal method body worked correctly.

Root cause

The language server's SemanticModel local-scope machinery (SemanticLookup.cs) was keyed exclusively on FunctionDeclarationSyntax. G# constructors are ConstructorDeclarationSyntax, and their synthesized FunctionSymbol has a null Declaration. As a result the hover/semantic-lookup pipeline never descended into constructor bodies:

• Constructor parameters and the implicit this were never registered in the scope maps.
• Constructor body locals were skipped in MapLocalVariables because the bound function's Declaration was null.
• Resolve's by-name local fallback (FindContainingFunction) and the implicit-this member resolution (ResolveImplicitThisMember) only considered method declarations, so bare local/member references inside init never resolved.

Fix

Generalized the local-declarations scope key from FunctionDeclarationSyntax to SyntaxNode and threaded constructors through the same pipeline that already powers method bodies:

• Map constructor parameters and the implicit this in the struct member loop (alongside methods).
• Match constructor body locals against the constructor's body syntax in MapLocalVariables, using a FunctionSymbol -> ConstructorDeclarationSyntax reverse map to recover the declaring syntax.
• Collect ConstructorDeclarationSyntax into per-file buckets and add FindContainingConstructor, so Resolve's by-name fallback covers constructor scopes.
• Extend ResolveImplicitThisMember to treat init(...) bodies as having an implicit this receiver, so bare member references (e.g. Area = product) resolve to the class member.

Hover for locals, constructor parameters, and class members inside init now matches method-body behavior exactly.

Tests

Added test/LanguageServer.Tests/Issue894ConstructorHoverTests.cs with regression coverage for:

• hover over a local variable declared in init -> (local variable) product int32
• hover over a constructor parameter -> (parameter) w int32
• hover over a class member referenced in init -> Area int32 + its doc comment

All three failed (null hover) before the fix and pass after.

Validation

• dotnet build GSharp.sln --configuration Release --no-restore -graph -> succeeded, 0 warnings/errors.
• dotnet test GSharp.sln --configuration Release --no-build -> 5490 passed, 1 skipped, 0 failed (Core 3340 +1 skipped, Compiler 1360, LanguageServer 340, Interpreter 308, Extensions 104, Sdk 38).