[SE-0095] Initial parsing implementation for '&' composition syntax
[SE-0095] Initial parsing implementation for '&' composition syntax

This commit defines the ‘Any’ keyword, implements parsing for composing
types with an infix ‘&’, and provides a fixit to convert ‘protocol<>’

- Updated tests & stdlib for new composition syntax
- Provide errors when compositions used in inheritance.
Any is treated as a contextual keyword. The name ‘Any’
is used emit the empty composition type. We have to
stop user declaring top level types spelled ‘Any’ too.

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation