Set SYSTEM_VERSION_COMPAT in LSEnvironment

macOS Big Sur lies about its version number to apps
built with SDKs earlier than the 11.0 SDK. We already
have code (daad98ce)
to undo that lie for version functions that return
numbers, but the version functions that return a
human-readable string were still lying.

Set SYSTEM_VERSION_COMPAT to fix the lie of that
string.

SYSTEM_VERSION_COMPAT alone is not adequate; it has
no effect on tests that do not share that Info.plist
and that we do not go through the trouble of giving
Info.plists because they are not bundled. But at
least for the Chromium app launched by Launch Services
we can improve system version number display.

Fixed: 1141569
Bug: 1108832
Change-Id: If064037bbb27ad42198bdebaf687e90e526e8751
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495266
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Auto-Submit: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820309}

chrome/app/app-Info.plist

@@ -235,6 +235,8 @@
 	<dict>
 		<key>MallocNanoZone</key>
 		<string>0</string>
+		<key>SYSTEM_VERSION_COMPAT</key>
+		<string>0</string>
 	</dict>
 	<key>LSFileQuarantineEnabled</key>
 	<true/>