swift234

Refactor most of the definitions of SILType methods into SILType.cpp.

Currently SILType's method definitions are strewn in various files in
lib/SIL/*.cpp. This patch just adds a new file SILType.cpp that centralizes
many of those definitions.

*NOTE* Any method which uses declarations inside of a specific *.cpp file I left
alone (there were 3). If we want to, we can perhaps create a new header to share
the interface in between the two. I wanted this change to be as incremental as
possible so I left that undone.

Swift SVN r11890