Style: Partially apply clang-tidy's cppcoreguidelines-pro-type-member-init

Didn't commit all the changes where it wants to initialize a struct
with `{}`. Should be reviewed in a separate PR.

Option `IgnoreArrays` enabled for now to be conservative, can be
disabled to see if it proposes more useful changes.

Also fixed manually a handful of other missing initializations / moved
some from constructors.

servers/rendering/renderer_rd/renderer_compositor_rd.cpp

@@ -286,7 +286,6 @@ RendererCompositorRD::RendererCompositorRD() {
 	}
 
 	singleton = this;
-	time = 0;
 
 	texture_storage = memnew(RendererRD::TextureStorage);
 	material_storage = memnew(RendererRD::MaterialStorage);