refactor: remove InspectableWebContentsViewMac in favor of the Views version

[nornagon]

Description of Change

I just deleted the Mac version and things seem to work okay? A bit surprising.
Probably I missed something?

Checklist

• PR description included and stakeholders cc'd
• npm test passes

Release Notes

Notes: none

[nornagon]

Looks like this regresses #37301, which was fixed by #37386. Fixed.

[nornagon]

Spent a day tracking down why the frame subscriber tests were failing. It looks like there's logic to skip rendering when the window is hidden unless headless mode is enabled: https://source.chromium.org/chromium/chromium/src/+/main:ui/views/cocoa/native_widget_mac_ns_window_host.mm;l=634-635;drc=3eb9fd518875bee685ad2e8c2b699822a8dfd5d9

  if (is_visible_ || is_headless_mode_window_)
    compositor_->Unsuspend();

i.e., if the window is hidden, the compositor won't unsuspend unless the headless bit is set.

The effects of setting the headless bit appear (currently) to be only this and one other thing: the frame size won't be constrained to a screen (https://source.chromium.org/chromium/chromium/src/+/main:components/remote_cocoa/app_shim/native_widget_mac_nswindow.mm;l=322-326;drc=2245eaf45d235260c18959d54844d6acc9fb4556). So I added some extra logic to unset the headless bit if we're visible in that function.

[zcbenz]

This puts Electron's WebContents in a views::WebView, which I think might cause some behavior changes, but this refactoring surely worths the little risk.

[nornagon]

Let's find out :D

[release-clerk]

No Release Notes