Expose Signature.thisParameter (#53628)

Co-authored-by: Nathan Shively-Sanders <293473+sandersn@users.noreply.github.com>

Author: Gerrit0

src/compiler/types.ts

@@ -6694,7 +6694,6 @@ export interface Signature {
     declaration?: SignatureDeclaration | JSDocSignature; // Originating declaration
     typeParameters?: readonly TypeParameter[];   // Type parameters (undefined if non-generic)
     parameters: readonly Symbol[];               // Parameters
-    /** @internal */
     thisParameter?: Symbol;             // symbol of this-type parameter
     /** @internal */
     // See comment in `instantiateSignature` for why these are set lazily.

tests/baselines/reference/api/typescript.d.ts

@@ -7313,6 +7313,7 @@ declare namespace ts {
         declaration?: SignatureDeclaration | JSDocSignature;
         typeParameters?: readonly TypeParameter[];
         parameters: readonly Symbol[];
+        thisParameter?: Symbol;
     }
     interface Signature {
         getDeclaration(): SignatureDeclaration;