[XProto] Fix X11KeyboardImpl::ChangeKeyMapping

This fixes a regression after [1].  The issue is that
GetKeySymsForUnicode() doesn't handle all characters.  This CL ports
the relevant part of XStringToKeysym() to match the behavior before the
regression.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2436787/5/remoting/host/linux/x11_keyboard_impl.cc#108

R=rkjnsn

Bug: 1144251
Change-Id: I91a3d42d0029e57c9e5a8cb8ee74b7bc76c00100
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518282Reviewed-by: Erik Jensen <rkjnsn@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Erik Jensen <rkjnsn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823782}

remoting/host/linux/x11_keyboard_impl.cc

@@ -42,6 +42,16 @@ bool FindKeycodeForKeySym(x11::Connection* connection,
   return false;
 }
 
+// This is ported from XStringToKeysym
+// https://gitlab.freedesktop.org/xorg/lib/libx11/-/blob/2b7598221d87049d03e9a95fcb541c37c8728184/src/StrKeysym.c#L147-154
+uint32_t UnicodeToKeysym(uint32_t u) {
+  if (u > 0x10ffff || u < 0x20 || (u > 0x7e && u < 0xa0))
+    return 0;
+  if (u < 0x100)
+    return u;
+  return u | 0x01000000;
+}
+
 }  // namespace
 
 namespace remoting {
@@ -101,11 +111,11 @@ bool X11KeyboardImpl::FindKeycode(uint32_t code_point,
 }
 
 bool X11KeyboardImpl::ChangeKeyMapping(uint32_t keycode, uint32_t code_point) {
-  bool res = false;
-  if (code_point > 0) {
-    for (auto keysym : GetKeySymsForUnicode(code_point)) {
-      if (keysym > 0xffff)
-        continue;
+  if (!code_point)
+    return false;
+  auto keysym = UnicodeToKeysym(code_point);
+  if (!keysym)
+    return false;
   connection_->ChangeKeyboardMapping({
       .keycode_count = 1,
       .first_keycode = static_cast<x11::KeyCode>(keycode),
@@ -113,10 +123,7 @@ bool X11KeyboardImpl::ChangeKeyMapping(uint32_t keycode, uint32_t code_point) {
       .keysyms = {static_cast<x11::KeySym>(keysym) /* lower-case */,
                   static_cast<x11::KeySym>(keysym) /* upper-case */},
   });
-      res = true;
-    }
-  }
-  return res;
+  return true;
 }
 
 void X11KeyboardImpl::Flush() {