[analyzer] Add support for escape of const pointers and use it to allow “newed” pointers to escape

Add a new callback that notifies checkers when a const pointer escapes. Currently, this only works
for const pointers passed as a top level parameter into a function. We need to differentiate the const
pointers escape from regular escape since the content pointed by const pointer will not change;
if it’s a file handle, a file cannot be closed; but delete is allowed on const pointers.

This should suppress several false positives reported by the NewDelete checker on llvm codebase.

llvm-svn: 178310