perf lock: Retrieve owner callstack in bpf program

This implements per-callstack aggregation of lock owners in addition to
per-thread.  The owner callstack is captured using `bpf_get_task_stack()`
at `contention_begin()` and it also adds a custom stackid function for the
owner stacks to be compared easily.

The owner info is kept in a hash map using lock addr as a key to handle
multiple waiters for the same lock.  At `contention_end()`, it updates the
owner lock stat based on the info that was saved at `contention_begin()`.
If there are more waiters, it'd update the owner pid to itself as
`contention_end()` means it gets the lock now.  But it also needs to check
the return value of the lock function in case task was killed by a signal
or something.

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
Tested-by: Athira Rajeev <atrajeev@linux.ibm.com>
Link: https://lore.kernel.org/r/20250227003359.732948-3-ctshao@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

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