Test integration of PartitionAlloc/HardenedPartitionAlloc in Tor Browser

PartitionAlloc/HardenedPartitionAlloc (https://github.com/struct/HardenedPartitionAlloc) have some interesting security properties we like to use (see: #20998 (moved) for a similar ticket wrt jemalloc). We should try to test them and compare them to jemalloc with partitioning enabled.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information