Move most version variable out to relase configs.

This allows finer control of the version variables
per release config, and removes a lot of computed
logic in favor of just directly setting the values.

Bug: 306702353
Test: lunch <device>-next-userdebug && m -j98
Change-Id: I9edc7171d124f0cfa540fea6f0e06ba877910444
Ignore-AOSP-First: Changes in internal projects first.
Merged-In: I9edc7171d124f0cfa540fea6f0e06ba877910444