chore: Rework mem2reg load & store removal #15011

Job	Run time
build-acvm-js	1m 23s
build-nargo	2m 23s
build-noirc-abi	1m 46s
build-noir-wasm	3m 46s
ACVM JS (Node.js)	37s
ACVM JS (Browser)	1m 44s
noirc_abi	2m 19s
Example scripts	12s
Noir JS	1m 11s
noir_codegen	1m 3s
Check external repo - ${{ matrix.project.repo }}	0s
Integration Tests (Browser)	2m 17s
Integration Tests (Node)	2m 32s
noir_wasm	1m 29s
End	1s
	22m 43s

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