Add --go-module-name flag to support generating Go module compatible code (#7651)

* Add --go-module-name flag to support generating code for go modules

* Rename echo example folder

* Grammar

* Update readme for go-echo example

* Update readme for go-echo example

* Re-enable go modules after test is done

examples/go-echo/hero/Warrior.go

@@ -0,0 +1,93 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package hero
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type WarriorT struct {
+	Name string `json:"name"`
+	Hp uint32 `json:"hp"`
+}
+
+func (t *WarriorT) Pack(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	if t == nil { return 0 }
+	nameOffset := builder.CreateString(t.Name)
+	WarriorStart(builder)
+	WarriorAddName(builder, nameOffset)
+	WarriorAddHp(builder, t.Hp)
+	return WarriorEnd(builder)
+}
+
+func (rcv *Warrior) UnPackTo(t *WarriorT) {
+	t.Name = string(rcv.Name())
+	t.Hp = rcv.Hp()
+}
+
+func (rcv *Warrior) UnPack() *WarriorT {
+	if rcv == nil { return nil }
+	t := &WarriorT{}
+	rcv.UnPackTo(t)
+	return t
+}
+
+type Warrior struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsWarrior(buf []byte, offset flatbuffers.UOffsetT) *Warrior {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &Warrior{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func GetSizePrefixedRootAsWarrior(buf []byte, offset flatbuffers.UOffsetT) *Warrior {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &Warrior{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func (rcv *Warrior) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *Warrior) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *Warrior) Name() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *Warrior) Hp() uint32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.GetUint32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *Warrior) MutateHp(n uint32) bool {
+	return rcv._tab.MutateUint32Slot(6, n)
+}
+
+func WarriorStart(builder *flatbuffers.Builder) {
+	builder.StartObject(2)
+}
+func WarriorAddName(builder *flatbuffers.Builder, name flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(name), 0)
+}
+func WarriorAddHp(builder *flatbuffers.Builder, hp uint32) {
+	builder.PrependUint32Slot(1, hp, 0)
+}
+func WarriorEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}