Perfprofd: Add parallel processing to stack script

Allow to process multiple proto files in parallel. This will fork
out each processed file into a subprocess, as making symbolization
thread-safe is non-trivial.

(cherry picked from commit 34c434d468d71e83b4ba9d69b1143c993ae1829e)

Bug: 73175642
Test: manual
Merged-In: I9bda1717e3f50569ad43f457413c7bc5831fd6a5
Change-Id: I9bda1717e3f50569ad43f457413c7bc5831fd6a5
1 file changed