Improve meson build.

-Add all required packages as wrap dependencies
-Move source lsitnings to separate files
-Proper dependencies declarations
-Set global D compiler arguments
-Add few asserts
-Add test exe
-Other small improvements

Tested with dmd with betterC, demos executable has to be run from 'demos' directory to properly load assets.

demos/utils/source/ecs_utils/meson.build

@@ -0,0 +1,18 @@
+utils_src += files(
+	'gfx/mesh.d',
+	'gfx/sprite.d',
+	'gfx/mesh_module.d',
+	'gfx/material.d',
+	'gfx/shader.d',
+	'gfx/vertex.d',
+	'gfx/config.d',
+	'gfx/buffer.d',
+	'gfx/render_list.d',
+	'gfx/renderer.d',
+	'gfx/texture.d',
+	'utils.d',
+	'math/matrix.d',
+	'math/vector.d',
+	'imgui_styles.d',
+	'imgui_bind.d',
+)