Add a Controller section to Setup with an on-screen pad editor

The on-screen pad is now placed from the panel's physical size: the
sticks and face buttons sit at the two-thumb rest point (about 17% of
the width inboard, 28% of the height up, clamped in millimetres), with
the d-pad and right stick below-inboard, shoulders above, and nothing
ever placed off screen or under a display cutout. Button sizes are
unchanged.

Setup > Controller holds the on-screen controls mode, a tint (Steam
blue #1A9FFF by default), opacity, button size, stick click (double-tap
for L3/R3), a full-screen layout editor, per-button mapping including
LT/RT, and resets for each.

Also from WinNative #772: the fakeinput ring poll backoff is capped at
2 ms instead of 16 ms, the session asks for unbuffered joystick input,
and the on-screen controls request unbuffered dispatch per gesture and
release everything when detached. The QAM button no longer draws at the
top-left corner in full-pad mode.

app/src/main/cpp/fakeinput_steam.cpp

@@ -1231,6 +1231,8 @@ EXPORT int close(int fd) {
   return my_close(fd);
 }
 
+static constexpr int kMaxRingWaitMs = 2;
+
 EXPORT ssize_t read(int fd, void *buf, size_t count) {
   std::unique_lock<std::recursive_mutex> guard(controller_mutex());
   auto controller = controller_map().find(fd);
@@ -1323,7 +1325,7 @@ EXPORT ssize_t read(int fd, void *buf, size_t count) {
     int result = nanosleep(&sleep_time, nullptr);
     guard.lock();
     if (result < 0) return -1;
-    if (backoff_ns < 16 * 1000 * 1000) backoff_ns *= 2;
+    if (backoff_ns < kMaxRingWaitMs * 1000 * 1000) backoff_ns *= 2;
   }
 }
 
@@ -1469,7 +1471,7 @@ static int poll_fake(struct pollfd *fds, nfds_t nfds, int timeout,
     if (deadline_ms >= 0 && monotonic_ms() >= deadline_ms)
       return 0;
 
-    if (backoff_ms < 16)
+    if (backoff_ms < kMaxRingWaitMs)
       backoff_ms *= 2;
   }
 }
@@ -1644,7 +1646,7 @@ EXPORT int select(int nfds, fd_set *readfds, fd_set *writefds,
     if (deadline_ms >= 0 && monotonic_ms() >= deadline_ms)
       return 0;
 
-    if (backoff_ms < 16)
+    if (backoff_ms < kMaxRingWaitMs)
       backoff_ms *= 2;
   }
 }