[Go] Object API support (#5339)

* start

* works for current usages!

* unpack: vector of struct

* optimize byte slice

* support nested struct

* support null table

* support struct

* support union

* update generated code

* grumble

* fix compiler warning

* update generated code

* wrap type in namespace

* bug

* wrap in namespace

* enum byte arrays

* generate struct for unions

* basic testing

* remove branching

* fix assert

* pack vector of fixed structs correctly

* omit null vectors

* Refactor Union Pack and UnPack methods

Remove append usage to increase code efficiency when dealing with large vectors

* generate goldens

tests/MyGame/Example/Test.go

@@ -6,6 +6,23 @@ import (
 	flatbuffers "github.com/google/flatbuffers/go"
 )
 
+type TestT struct {
+	A int16
+	B int8
+}
+
+func TestPack(builder *flatbuffers.Builder, t *TestT) flatbuffers.UOffsetT {
+	if t == nil { return 0 }
+	return CreateTest(builder, t.A, t.B)
+}
+func (rcv *Test) UnPack() *TestT {
+	if rcv == nil { return nil }
+	t := &TestT{}
+	t.A = rcv.A()
+	t.B = rcv.B()
+	return t
+}
+
 type Test struct {
 	_tab flatbuffers.Struct
 }