refactor: change defined(MAS_BUILD) to IS_MAS_BUILD() (#36332)

* refactor: change defined(MAS_BUILD) to IS_MAS_BUILD()

This is missing-definition safe and thus allows us to move the definition of this macro away from "all compilation targets" to "just the compilation targets that depend on this macro".

In turn this makes the rebuild time changing from mas <-> darwin only 80 seconds on my machine, instead of the 12-15 minutes it used to take.  This will also allow us in the future to build both MAS and darwin on the same CI machine.  Costing us ~2 minutes on one machine but saving us anywhere from 30 minutes to an hour of CI time on other parts of the matrix.

* build: always define IS_MAS_BUILD even on non-mac builds

* build: use extra_configs

patches/chromium/disable_compositor_recycling.patch

@@ -6,7 +6,7 @@ Subject: fix: disabling compositor recycling
 Compositor recycling is useful for Chrome because there can be many tabs and spinning up a compositor for each one would be costly. In practice, Chrome uses the parent compositor code path of browser_compositor_view_mac.mm; the NSView of each tab is detached when it's hidden and attached when it's shown. For Electron, there is no parent compositor, so we're forced into the "own compositor" code path, which seems to be non-optimal and pretty ruthless in terms of the release of resources. Electron has no real concept of multiple tabs per window, so it should be okay to disable this ruthless recycling altogether in Electron.
 
 diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
-index a420b3cf9b1c325967318db322d61c4ebc4cf7c6..c5bc07973bba93aff7837cea92895e2ef7dff897 100644
+index cc2836fb66d9cf84fa298f1d75480f2c796b274f..4de5eddfeded8881717832c78725eb57769dcb5b 100644
 --- a/content/browser/renderer_host/render_widget_host_view_mac.mm
 +++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
 @@ -525,7 +525,11 @@