csharp: extract this./base.-qualified member calls

[pbednarcik]

this.Foo() and base.Foo() currently emit no call edge at all — both member-call query patterns capture the receiver with expression: (_), but this and base are anonymous tokens in tree-sitter-c-sharp, and a named-node wildcard never matches them. Every qualified self/base call in a C# codebase silently vanishes from the graph (noticeable on base.OnActionExecuting(...)-style overrides, which are everywhere in ASP.NET code).

Fix (extraction only, resolver untouched):

• Two new query alternations match the anonymous token literally ((member_access_expression "this" name: (identifier)) and the base twin).
• The receiver type is resolved at capture time from the enclosing declaration — this → the innermost type's name, base → its declared base class (discrimination mirrors emitCSharpBaseList: first base-list entry that is a ctor-base or not I-prefixed; structs and interface-only bases stamp nothing and the call still emits as a plain member_call).
• The stamped receiver_type then rides the existing receiver-typed member binding path, so this.Foo() binds the hiding member and base.Foo() the base member with no new resolver machinery.

Tests: extractor spec (edges + receiver_type stamps for both qualifiers, new-hiding case) and an end-to-end resolver spec (this.Foo() → hiding member, base.Foo() → base member). Both watched red before the fix. internal/parser/languages fully green; internal/resolver and internal/indexer at their pre-existing Windows baselines with zero new failures.

The second commit bumps the csharp extractor version 3→4 so existing stores restage .cs files and grow the new edges. Validated live on a counted C# fixture repo via exactly that path — binary swap, no store wipe, salt-triggered restage — with both call shapes binding their compiler-correct targets (this.X() → the new-hiding member, base.X() → the base member) at 0.95 with receiver_type stamped.

[zzet]

Two adjacent gaps found (inspired by PR, not directly related to PR)

• this?.Foo() / base?.Foo() emits nothing — the conditional-access pattern has the identical condition: (_) blindness. Rare in practice (this is never null), but it's the same bug left half-fixed.

• C# records emit no member nodes at all. public record Tower(int N) { public int Chime() {...} } produces a type node and its extends edge, and nothing else — every method in every record is invisible to the graph, so no call edges leave them. Records are idiomatic C# 9+, so this is a substantially bigger gap than the one this PR closes.