[objcmt] Rewrite [NSNumber numberWith*] messages to the new @() boxing syntax.

There are some caveats:
-If an implicit cast (e.g. int -> float for numberWithFloat:) was required, the message
 will not get rewritten
-If the message was with numberWithInteger:/numberWithUnsignedInteger:, which are very
 commonly used, be more liberal and allow the boxing syntax if the underlying type has
 same signedness and will not lose precision.

Part of rdar://11438360

llvm-svn: 156844