meson: include VkLayer_MESA_overlay in the devenv

See https://github.com/KhronosGroup/Vulkan-Loader/blob/main/docs/LoaderLayerInterface.md#linux-layer-discovery

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35650>

src/vulkan/overlay-layer/VkLayer_MESA_overlay.json.in

@@ -3,7 +3,7 @@
     "layer" : {
         "name": "VK_LAYER_MESA_overlay",
         "type": "GLOBAL",
-        "library_path": "libVkLayer_MESA_overlay.so",
+        "library_path": "@library_path@",
         "api_version": "1.4.303",
         "implementation_version": "1",
         "description": "Mesa Overlay layer"

src/vulkan/overlay-layer/meson.build

@@ -36,12 +36,22 @@ vklayer_mesa_overlay = shared_library(
   install : true
 )
 
-install_data(
-  files('VkLayer_MESA_overlay.json'),
+configure_file(
+  configuration : {'library_path' : 'libVkLayer_MESA_overlay.so'},
+  input : 'VkLayer_MESA_overlay.json.in',
+  output : '@BASENAME@',
+  install : true,
   install_dir : join_paths(get_option('datadir'), 'vulkan', 'explicit_layer.d'),
   install_tag : 'runtime',
 )
 
+configure_file(
+  configuration : {'library_path' : vklayer_mesa_overlay.full_path()},
+  input : 'VkLayer_MESA_overlay.json.in',
+  output : '@PLAINNAME@_dev.json',
+)
+devenv.append('VK_ADD_LAYER_PATH', meson.current_build_dir())
+
 install_data(
   'mesa-overlay-control.py',
   install_dir : get_option('bindir'),