parser: Make list of arbitrary substitution functions configurable. (… #399

Job	Run time
Linux (nightly, --features dummy_match_byte)	2m 12s
Linux (stable, --features dummy_match_byte)	43s
Linux (nightly, --features malloc_size_of)	2m 9s
Linux (nightly)	2m 19s
Linux (1.68.0)	6m 10s
Linux (beta)	33s
Linux (beta, --features malloc_size_of)	35s
Linux (stable, --features malloc_size_of)	42s
Linux (nightly, --features bench,dummy_match_byte)	4m 41s
Linux (1.68.0, --features dummy_match_byte)	6m 41s
Linux (nightly, --features bench)	5m 22s
Linux (beta, --features dummy_match_byte)	31s
Linux (stable)	37s
Linux (1.68.0, --features malloc_size_of)	6m 16s
Result	2s
	39m 33s

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