Update ts codegen (#8421)

Makes the return type of `static getFullyQualifiedName()` be a string literal instead of just the string type

Update tests

Co-authored-by: Björn Harrtell <bjornharrtell@users.noreply.github.com>

tests/ts/optional-scalars/scalar-stuff.ts

@@ -209,7 +209,7 @@ defaultEnum():OptionalByte {
   return offset ? this.bb!.readInt8(this.bb_pos + offset) : OptionalByte.One;
 }
 
-static getFullyQualifiedName():string {
+static getFullyQualifiedName(): "optional_scalars.ScalarStuff" {
   return 'optional_scalars.ScalarStuff';
 }