Fix #1453: use 64-bit variables for RPR to prevent overflow

Overflow may occur in corner cases in large pictures.
Added const modifiers where appropriate.
Defined additional variables to hold intermediate values to avoid
code duplication.
Rename variables to more closely match VVC specification.
6 jobs for !2008 with fix1453 in 53 minutes and 1 second (queued for 19 seconds)
detached
Status Job ID Name Coverage
  Build
passed #20325
macos
build_macos

00:33:32

passed #20326
ubuntu1604
build_ubuntu1604

00:00:57

passed #20327
ubuntu1804
build_ubuntu1804

00:02:19

passed #20328
ubuntu1804-gcc8
build_ubuntu1804-gcc8

00:01:01

passed #20329
vc191x
build_vc191x

00:15:27

passed #20330
vc192x
build_vc192x

00:13:54