Fix go generator undefined Package name, also throwing exception (#7632)

* Fix go generator undefined Package, also throw exception in specific examples.

* Add test for go generator import problem

* Add new version of generated go file. Fix conflict.

* Add executable permission to generate_code.py script.

* Improve test quality, remove unwanted generated files, better naming

* Fix comments

* clang format

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

tests/Pizza.go

@@ -0,0 +1,78 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package Pizza
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type PizzaT struct {
+	Size int32 `json:"size"`
+}
+
+func (t *PizzaT) Pack(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	if t == nil { return 0 }
+	PizzaStart(builder)
+	PizzaAddSize(builder, t.Size)
+	return PizzaEnd(builder)
+}
+
+func (rcv *Pizza) UnPackTo(t *PizzaT) {
+	t.Size = rcv.Size()
+}
+
+func (rcv *Pizza) UnPack() *PizzaT {
+	if rcv == nil { return nil }
+	t := &PizzaT{}
+	rcv.UnPackTo(t)
+	return t
+}
+
+type Pizza struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsPizza(buf []byte, offset flatbuffers.UOffsetT) *Pizza {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &Pizza{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func GetSizePrefixedRootAsPizza(buf []byte, offset flatbuffers.UOffsetT) *Pizza {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &Pizza{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func (rcv *Pizza) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *Pizza) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *Pizza) Size() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *Pizza) MutateSize(n int32) bool {
+	return rcv._tab.MutateInt32Slot(4, n)
+}
+
+func PizzaStart(builder *flatbuffers.Builder) {
+	builder.StartObject(1)
+}
+func PizzaAddSize(builder *flatbuffers.Builder, size int32) {
+	builder.PrependInt32Slot(0, size, 0)
+}
+func PizzaEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}