[TS]: builder, Fix requiredField(). Verity that the field is present in the vtable (#7739) (#7752)

* [TS]: Fix vtable creation for consecutive required fileds (#7739)

* handle feedback

* comment the schema

* comment change in builder.ts

* [TS]: builder, Fix requiredField()

Verifty that the field is present in the vtable.

* restore monsterdata binary file

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

tests/required_strings.fbs

@@ -0,0 +1,12 @@
+namespace required_strings;
+
+/**
+ * Foo defines a type where both fields are mandatory.
+ * The creation of a Foo buffer must throw if either of the fields is missing.
+ *
+ * https://github.com/google/flatbuffers/issues/7739
+ */
+table Foo {
+  str_a:string (required);
+  str_b:string (required);
+}