[HLE] Fix guest-thread sync and boot for Unreal Engine titles (#102)

* [HLE] Fix guest-thread sync and boot for Unreal Engine titles

Silent Hill: The Short Message (and other UE titles) now boot the full
engine thread graph instead of hanging early. Four related fixes:

- pthread cond/mutex semantics: retain a signal raised with no waiter as
  pending, and key block/wake on the state's identity rather than a
  resolved address that could differ between lock and unlock. This ends
  the ~1.5M-call cond_wait busy-spin.

- Warm HLE type initializers and force-JIT their methods on a host thread
  at Freeze(). A .cctor or first-time JIT running on a guest thread's
  hijacked stack fail-fasts the CLR as "Invalid Program: attempted to
  call a UnmanagedCallersOnly method from managed code".

- Guest thread scheduling: pump after a wake so a readied thread actually
  runs, add a dispatcher thread for when every guest thread is parked,
  and make the pump-depth guard an atomic CAS.

- Route mutex/rwlock lock/unlock off the non-blocking leaf-import fast
  path so a contended lock can deschedule its guest thread.

Ported from the unreal-boot-fixes branch.

* [HLE] Keep mutex/rwlock unlock on the leaf-import fast path

The previous change routed all mutex/rwlock lock and unlock NIDs off the
leaf fast path so a contended lock could deschedule its guest thread. But
unlock never blocks, and taking it off the fast path made it slow enough
that Demon's Souls' job workers livelocked in a guest spinlock (millions
of mutex_unlock calls, no import progress, main thread stuck in
sceKernelWaitEventFlag).

Only *lock* needs to leave the leaf path. Restore the four unlock NIDs
(mutex + rwlock) so guest spinlocks stay cheap, while lock/rd/wrlock
remain off it for the blocking case Silent Hill needs.

* [HLE] Gate pthread_mutex_lock guest-thread blocking (fixes Demon's Souls)

Re-enabling cooperative deschedule on a contended pthread_mutex_lock
regressed Demon's Souls: its job workers run on libSceFiber, and blocking
a guest thread mid-fiber left sceFiberSwitch returning ESRCH followed by
a null fiber-context deref (0xC0000005). Bisect confirmed the pthread
change as the cause; the game reaches the same point as before it once
the block is skipped.

Gate the block behind SHARPEMU_MUTEX_LOCK_BLOCKING (off by default) so
contended locks fall through to the synchronous host-thread wait. The
rest of the pthread fixes (cond_wait pending signals, identity wake keys)
are unaffected.

src/SharpEmu.Core/Cpu/Native/DirectExecutionBackend.Imports.cs

@@ -810,11 +810,14 @@ public sealed partial class DirectExecutionBackend
 			return !_logUsleep;
 		}
 
+		// Only mutex/rwlock *lock* is excluded: it may block a contended acquire, which the
+		// leaf path can't. unlock never blocks and stays here — routing it off the fast path
+		// slows guest spinlocks enough to livelock (Demon's Souls).
 		return nid is
-			"9UK1vLZQft4" or // scePthreadMutexLock
 			"tn3VlD0hG60" or // scePthreadMutexUnlock
-			"7H0iTOciTLo" or // pthread_mutex_lock
 			"2Z+PpY6CaJg" or // pthread_mutex_unlock
+			"EgmLo6EWgso" or // pthread_rwlock_unlock
+			"+L98PIbGttk" or // scePthreadRwlockUnlock
 			"8aI7R7WaOlc" or // sceAmprCommandBufferConstructor
 			"zgXifHT9ErY" or // sceVideoOutIsFlipPending
 			"V++UgBtQhn0" or // sceAgcGetDataPacketPayloadAddress
@@ -888,12 +891,7 @@ public sealed partial class DirectExecutionBackend
 			"6ULAa0fq4jA" or // scePthreadRwlockInit
 			"1471ajPzxh0" or // pthread_rwlock_destroy
 			"BB+kb08Tl9A" or // scePthreadRwlockDestroy
-			"iGjsr1WAtI0" or // pthread_rwlock_rdlock
-			"Ox9i0c7L5w0" or // scePthreadRwlockRdlock
-			"sIlRvQqsN2Y" or // pthread_rwlock_wrlock
-			"mqdNorrB+gI" or // scePthreadRwlockWrlock
-			"EgmLo6EWgso" or // pthread_rwlock_unlock
-			"+L98PIbGttk" or // scePthreadRwlockUnlock
+			// rwlock rd/wr lock removed (can block); init/destroy/unlock stay.
 			"aI+OeCz8xrQ" or // scePthreadSelf
 			"EotR8a3ASf4" or // pthread_self
 			"eoht7mQOCmo" or // scePthreadGetspecific