lint: Check for missing braces

The `eek/layersurface.c` file should be excluded because it's an imported, "foreign" source, but clang-tidy doesn't seem to have an annotation for that.

An alternative would have been to exclude it in Meson and do the check there, but that requires clang-tidy, raising the barrier to contribute of Squeekboard even more (it already requires libfeedback, which isn't packaged widely).

meson.build

@@ -20,6 +20,7 @@ add_project_arguments(
     '-Werror=incompatible-pointer-types',
     '-Werror=int-conversion',
     '-Werror=redundant-decls',
+    '-Werror=parentheses',
     '-Wformat-nonliteral',
     '-Wformat-security',
     '-Winit-self',