[TS] Fix getFullyQualifiedName codegen for typescript (#7730)

#7451 caused getFullyQualifiedName to return a name with underscores,
not periods. Because the fully qualified name is a property of
FlatBuffers, not the language being codegen'd for, it should use
periods. Fixes #7564.

Co-authored-by: Derek Bailey <derekbailey@google.com>

tests/ts/reflection/field.js

@@ -155,7 +155,7 @@ export class Field {
         return true;
     }
     static getFullyQualifiedName() {
-        return 'reflection_Field';
+        return 'reflection.Field';
     }
     static startField(builder) {
         builder.startObject(13);