gh-106529: Implement POP_JUMP_IF_XXX uops (#106551)

gh-106529: Implement POP_JUMP_IF_XXX uops (#106551)

- Hand-written uops JUMP_IF_{TRUE,FALSE}.
  These peek at the top of the stack.
  The jump target (in superblock space) is absolute.

- Hand-written translation for POP_JUMP_IF_{TRUE,FALSE},
  assuming the jump is unlikely.
  Once we implement jump-likelihood profiling,
  we can implement the jump-unlikely case (in another PR).

- Tests (including some test cleanup).

- Improvements to len(ex) and ex[i] to expose the whole trace.