Bug 1811834 - Clean up nsWidgetInitData. r=cmartin,geckoview-reviewers,calu

Move it to the mozilla::widget namespace.

Use enum classes for transparency, popup type, popup level, etc.

Mostly automated with sed, but there were a few manual changes required
as well in windows code because they relied on Atomic<TransparencyMode>
working (which now doesn't because TransparencyMode is 1 byte instead of
4 bytes).

Differential Revision: https://phabricator.services.mozilla.com/D167537

gfx/layers/wr/WebRenderLayerManager.cpp

@@ -69,7 +69,7 @@ bool WebRenderLayerManager::Initialize(
   static bool hasInitialized = false;
 
   WindowKind windowKind;
-  if (mWidget->WindowType() != eWindowType_popup) {
+  if (mWidget->GetWindowType() != widget::WindowType::Popup) {
     windowKind = WindowKind::MAIN;
   } else {
     windowKind = WindowKind::SECONDARY;