Fixed typo

Fix mac build error

is => it

Also added simple (in-process) test.

Change-Id: I38580d554dd52f590e3396ec4846e07546dcf07d
Tested: on Linux.

Added new constants

Add new constants in Constants.java

All single ints int FlatBufferBuilder.java were replaced by constants
from Constants.java

pulling methods inside the class... so as to share wrapInNamespace later

This is useful because many JSON generators will sort the fields,
cause X_type to follow X.

Change-Id: I00ef3ac05418224fc05aee93e6b3b3597e73ffe3
Tested: on Linux.
Bug: 29221752

Also fixed most codegenerators using the wrong namespace when multiple
namespace were used in a file, with some files not being generated.

Change-Id: Ib42969221239d7244e431cbd667ef69200fc415f
Tested: on Linux.
Bug: 29338474

Fix test using compat.binary_types (from March).

e.g.: { myfield: cos(rad(180)) } is equivalent to writing { myfield: -1.0 }

Bug: 29338398
Change-Id: I6fc4ef1fd10bda3ba78cba464414dd071a2f50ca
Tested: on Linux.

Bug: 29337887, 29336299
Change-Id: Iad8b3b2263f6cea7ee7e45994369194960df293b
Tested: on Linux.

Namespace work

Add env var for flatc schema compiler cmake module

Change-Id: I8f9ef1d14f86671ced929c7a159115b1d8510327
Tested: on Linux.

Change-Id: I737f6fd0bb1302ab7cfa6ab8b06108e221ebb63c
Tested: on Linux.