scaling: Add GSettings for adjusting the height of the panel

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/679>

data/meson.build

@@ -1,5 +1,37 @@
 gnome = import('gnome')
 
+#workaround due to https://github.com/mesonbuild/meson/issues/1687
+copy_schema = custom_target('copy-gschema-to-builddir',
+  input: 'sm.puri.Squeekboard.gschema.xml',
+  output: 'sm.puri.Squeekboard.gschema.xml',
+  command: ['cp', '@INPUT@', '@OUTPUT@']
+)
+schemas = ['sm.puri.Squeekboard.gschema.xml']
+compile_schemas = custom_target('glib-compile-schemas',
+  build_by_default: true,
+  output: 'gschemas.compiled',
+  install: false,
+  command: [find_program('glib-compile-schemas'),
+    meson.current_build_dir()
+  ],
+  depends: [copy_schema]
+)
+install_data(
+  schemas,
+  install_dir: schemasdir
+)
+
+compile_schemas = find_program('glib-compile-schemas', required: false)
+if compile_schemas.found()
+  test('Validate schema file', compile_schemas,
+       args: ['--strict', '--dry-run', meson.current_source_dir()])
+endif
+
+install_data(
+  schemas,
+  install_dir: 'share/glib-2.0/schemas'
+)
+
 squeekboard_resources = gnome.compile_resources(
    'squeekboard-resources',
    'squeekboard.gresources.xml',