Debugger: Cleanups, no functional change.
Debugger: Implement #9946.

TableCellValueRenderer{Utils}:
- The rendering calls now take a boolean indicating if the value
  being rendered differs from its previous state. This is taken
  into account by rendering it in a different color to indicate
  the change. Adjust all implementing subclasses accordingly.

VariablesView::ModelNode:
- Now stores the previous value of the corresponding value node,
  and can be queried if its value has changed. Used by renderers.

VariablesView::_{Add,Apply}ViewStateDescendentInfos():
- When walking the model, also store/restore the values of nodes in the
  history.

In summation of all the above changes, when stepping through a function,
we now display values that have changed since the last step, or that have
appeared for the first time in a different color.
kernel: Sync panic messages across acquire_spinlock versions.

* Always include last caller and lock value on both UP and MP path.
* Change lock value printing to hex format, as 0xdeadbeef is more
  obvious than its decimal counterpart.
kernel: Also push lock caller in acquire_spinlock_nocheck.