Add bigger method type encodings to protocol objects. <rdar://problem/10492418>

The new metadata are method @encode strings with additional data.

1. Each Objective-C object is marked with its class name and protocol names.
The same is done for property @encode already.

2. Each block object is marked with its function prototype's @encoding. For
example, a method parameter that is a block object that itself returns void
and takes an int would look like:
    @?<v@?i>

These new method @encode strings are stored in a single array pointed to by structs protocol_t and objc_protocol_ext.

Patch provided by Greg Parker!

llvm-svn: 145469