Provide synthetic children for some vector types

Provide synthetic children for some vector types

Unlike GDB, we tackle the problem of representing vector types in different styles by having a synthetic child provider that recognizes the format you're trying to apply to the variable, and coming up with the right type and number of child values to match that format

This makes for a more compact representation and less visual noise

Fixes rdar://5429347

llvm-svn: 231449