This works in a single pass, and supports both toplevel and member
decorations. Includes support for 5 new opcodes:

- OpDecorate introduces a single decoration for a toplevel id.

- OpMemberDecorate introduces a single decoration for a <id,
  memberIndex> pair.

- OpDecorationGroup introduces a new value category which has no
  representation downstream at all. This is safely implemented by
  doing nothing at all [we don't need to be able to introspect later].

- OpGroupDecorate applies all decorations in a decoration group to each
  of a list of other ids.

- OpGroupMemberDecorate applies all decorations in a decoration group to
  each of a list of members (<id>, memberIndex pairs).

Bug: b/120799499

Change-Id: Iaea970b23348e70d57ddb96a4df0726cfb511e03
Reviewed-on: https://swiftshader-review.googlesource.com/c/23174Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>