agx: Detect conditional breaks

agx: Detect conditional breaks

Search for code like

   if ... {
      break
   }

and replace with a break_if pseudo-instruction for optimized handling, since the
break_if lowering is better than the original code.

   total instructions in shared programs: 1764596 -> 1764350 (-0.01%)
   instructions in affected programs: 24540 -> 24294 (-1.00%)
   helped: 78
   HURT: 0
   Instructions are helped.

   total bytes in shared programs: 11611196 -> 11610212 (<.01%)
   bytes in affected programs: 166458 -> 165474 (-0.59%)
   helped: 78
   HURT: 0
   Bytes are helped.

shader-db probably understates the benefit here, since this optimizes the body
of loops.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25052>