libobs: Add Wayland hotkey infrastructure

Users on Wayland are displeased that they cannot see their hotkey
bindings. This enables key reporting like X11, and has the infrastructure
in place in case Wayland ever decides to allow for capturing input.

cmake/Modules/FindXkbcommon.cmake

@@ -0,0 +1,37 @@
+# Once done these will be defined:
+#
+# XKBCOMMON_FOUND XKBCOMMON_INCLUDE_DIRS XKBCOMMON_LIBRARIES
+
+find_package(PkgConfig QUIET)
+if(PKG_CONFIG_FOUND)
+  pkg_check_modules(_XKBCOMMON QUIET xkbcommon)
+endif()
+
+find_path(
+  XKBCOMMON_INCLUDE_DIR
+  NAMES xkbcommon/xkbcommon.h
+  HINTS ${_XKBCOMMON_INCLUDE_DIRS}
+  PATHS /usr/include /usr/local/include /opt/local/include)
+
+find_library(
+  XKBCOMMON_LIB
+  NAMES xkbcommon libxkbcommon
+  HINTS ${_XKBCOMMON_LIBRARY_DIRS}
+  PATHS /usr/lib /usr/local/lib /opt/local/lib)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Xkbcommon DEFAULT_MSG XKBCOMMON_LIB
+                                  XKBCOMMON_INCLUDE_DIR)
+mark_as_advanced(XKBCOMMON_INCLUDE_DIR XKBCOMMON_LIB)
+
+if(XKBCOMMON_FOUND)
+  set(XKBCOMMON_INCLUDE_DIRS ${XKBCOMMON_INCLUDE_DIR})
+  set(XKBCOMMON_LIBRARIES ${XKBCOMMON_LIB})
+
+  if(NOT TARGET Xkbcommon::Xkbcommon)
+    add_library(Xkbcommon::Xkbcommon INTERFACE IMPORTED)
+    set_target_properties(
+      Xkbcommon::Xkbcommon PROPERTIES INTERFACE_INCLUDE_DIRECTORIES
+                                "${XKBCOMMON_INCLUDE_DIRS}")
+  endif()
+endif()