Import meson build files from an 3.22

Specifically, from 6dd6660c685d22e88af5ed4d0b5f1f22df0338de

gtk/inspector/meson.build

@@ -0,0 +1,31 @@
+inspector_sources = files(
+  'action-editor.c',
+  'actions.c',
+  'cellrenderergraph.c',
+  'css-editor.c',
+  'css-node-tree.c',
+  'data-list.c',
+  'general.c',
+  'gestures.c',
+  'graphdata.c',
+  'gtktreemodelcssnode.c',
+  'init.c',
+  'inspect-button.c',
+  'magnifier.c',
+  'menu.c',
+  'misc-info.c',
+  'object-hierarchy.c',
+  'object-tree.c',
+  'prop-editor.c',
+  'prop-list.c',
+  'resource-list.c',
+  'selector.c',
+  'signals-list.c',
+  'size-groups.c',
+  'statistics.c',
+  'treewalk.c',
+  'visual.c',
+  'window.c',
+  'strv-editor.c',
+  'gtkstackcombo.c'
+)