.. for concurrent OSR. There, the challenge is to hit the correct
JumpLoop bytecode once compilation completes, since execution has
moved on in the meantime.

This CL adds a new mechanism to request installation at a specific
bytecode offset. We add a new `osr_install_target` field to the
BytecodeArray:

  bitfield struct OSRUrgencyAndInstallTarget extends uint16 {
    osr_urgency: uint32: 3 bit;
    osr_install_target: uint32: 13 bit;
  }

  // [...]
  osr_urgency_and_install_target: OSRUrgencyAndInstallTarget;
  bytecode_age: uint16;  // Only 3 bits used.
  // [...]

Note urgency and install target are packed into one 16 bit field,
we can thus merge both checks into one comparison within JumpLoop.
Note also that these fields are adjacent to the bytecode age; we
still reset both OSR state and age with a single (now 32-bit)
store.

The install target is the lowest 13 bits of the bytecode offset.
When set, every reached JumpLoop will check `is this my offset?`,
and if yes, jump into runtime to tier up.

Drive-by: Rename BaselineAssembler::LoadByteField to LoadWord8Field.

Bug: v8:12161
Change-Id: I275d468b19df3a4816392a2fec0713a8d211ef80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3571812Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Linke <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79853}