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_scene_render_rd.cpp

@@ -3976,10 +3976,6 @@ RS::ShaderNativeSourceCode RendererSceneRenderRD::FogShaderData::get_native_sour
 	return scene_singleton->volumetric_fog.shader.version_get_native_source_code(version);
 }
 
-RendererSceneRenderRD::FogShaderData::FogShaderData() {
-	valid = false;
-}
-
 RendererSceneRenderRD::FogShaderData::~FogShaderData() {
 	RendererSceneRenderRD *scene_singleton = static_cast<RendererSceneRenderRD *>(RendererSceneRenderRD::singleton);
 	ERR_FAIL_COND(!scene_singleton);