Parsing from proto should keep field ID. (fixes #7645) (#7655)

* Parsing from proto should keep field ID. (fixes #7645)

* Fix failed tests

* Fix windows warning

* Improve attribute generation in proto to fbs

* Check if id is used twice. fix Some clang-format problems

* Test if fake id can solve the test problem

* Validate proto file in proto -> fbs generation.

* Fix error messages

* Ignore id in union

* Add keep proto id for legacy and check gap flag have been added. Reserved id will be checked.

* Add needed flags

* unit tests

* fix fromat problem. fix comments and error messages.

* clear

* More unit tests

* Fix windows build

* Fix include problems

* Fake commit to invoke rebuild

* Fix buzel build

* Fix some issues

* Fix comments, fix return value and sort for android NDK

* Fix return type

* Break down big function

* Place todo

---------

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

tests/prototest/test.proto

@@ -24,6 +24,7 @@ message ProtoMessage {
   // Ignored non-doc comment.
   // A nested message declaration, will be moved to top level in .fbs
   message OtherMessage {
+    reserved 2, 9 to 11, 15;
     optional double a = 26;
     /// doc comment for b.
     optional float b = 32 [default = 3.14149];
@@ -40,7 +41,7 @@ message ProtoMessage {
   }
   optional int32 c = 12 [default = 16];
   optional int64 d = 1 [default = 0];
-  optional uint32 p = 1;
+  optional uint32 p = 40;
   optional uint64 e = 2;
   /// doc comment for f.
   optional sint32 f = 3 [default = -1];
@@ -55,7 +56,7 @@ message ProtoMessage {
   /// lines
   required string l = 10;
   optional bytes m = 11;
-  optional OtherMessage n = 12;
+  optional OtherMessage n = 41;
   repeated string o = 14;
   optional ImportedMessage z = 16;
   /// doc comment for r.