Rewrite GRC::GetConstantBlockReward #2021

Job	Run time
Lint	44s
macOS 12 native [GOAL install] [GUI] [no depends]	12m 57s
ARM [GOAL install] [buster]	12m 52s
Win32	14m 34s
Win64	32m 20s
i386 Linux [GOAL install] [focal]	12m 53s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	17m 14s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	16m 8s
x86_64 Linux [ASan] [LSan] [UBSan] [integer] [jammy] [no depends]	19m 13s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [noble]	27m 47s
arm64 macOS 10.14 [GOAL deploy] [GUI] [no tests] [noble]	26m 44s
	3h 13m 26s

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