DebugInfo: Add MDTypeRefArray, to replace DITypeArray
DebugInfo: Add MDTypeRefArray, to replace DITypeArray

This array-like wrapper adapts `MDTuple` to have elements of `MDTypeRef`
(whereas `MDTypeArray` has elements of `MDType`).  This is necessary to
migrate code using `DITypeArray`.  The only use of this is
`MDSubroutineType`'s `getTypeArray()` accessor.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@234200 91177308-0d34-0410-b5e6-96231b3b80d8

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