[std] Various Int32 tweaks

Remove incorrect @:commutative in Int32
Change ops from public to private
Add some more inlines
Remove deprecated Int32 error message
Merge pull request #2697 from Herschel/int32-tweaks

[std] Various Int32 tweaks
[std] Rewrite Int64 as an abstract
[tests] Rewrite Int64 unit tests
[java] Implement abstract Int64
[cs] Implement abstract Int64