Add declaration_start parameter to DeclarationParser parse_value (#400) #348

Job	Run time
Linux (nightly)	2m 31s
Linux (nightly, --features dummy_match_byte)	2m 35s
Linux (beta)	33s
Linux (beta, --features dummy_match_byte)	33s
Linux (stable)	32s
Linux (stable, --features dummy_match_byte)	33s
Linux (1.63.0)	2m 48s
Linux (1.63.0, --features dummy_match_byte)	2m 50s
Linux (nightly, --features bench)	5m 55s
Linux (nightly, --features bench,dummy_match_byte)	5m 46s
Result	1s
	24m 37s

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