[PA] Scheduler-Loop Quarantine is configured via JSON

Remove `features::kPartitionAllocZappingByFreeFlags` and merge it with
`features::kPartitionAllocSchedulerLoopQuarantine` because they are
always used together. Also remove params
`kPartitionAllocSchedulerLoopQuarantineBranchCapacity` and
`kPartitionAllocSchedulerLoopQuarantineBrowserUICapacity`, and instead
add one combined string parameter
`kPartitionAllocSchedulerLoopQuarantineConfig`. It is more scalable as
we are going to adjust parameters per process.

Change-Id: I3c4f380ea304c32d6914317747202f36136942e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6790127
Reviewed-by: Lei Zhang <[email protected]>
Commit-Queue: Mikihito Matsuura <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1496362}
NOKEYCHECK=True
GitOrigin-RevId: 5f573cac5ae375d8080b84b64a4a9c292ee82379

Author: mikt

src/partition_alloc/scheduler_loop_quarantine.h

@@ -78,6 +78,8 @@ struct SchedulerLoopQuarantineConfig {
   bool leak_on_destruction = false;
   bool enable_quarantine = false;
   bool enable_zapping = false;
+  // For informational purposes only.
+  char branch_name[32] = "";
 };
 
 class PA_COMPONENT_EXPORT(PARTITION_ALLOC) SchedulerLoopQuarantineRoot {