tools/clang/codesearch: migrate dyn_cast to dyn_cast_if_present #19154

Job	Run time
gvisor	4m 9s
aux	3m 54s
build	4m 56s
old	7m 9s
race_dashboard	4m 35s
arch (presubmit_arch_netbsd)	4m 16s
race	8m 50s
arch (presubmit_arch_windows)	3m 43s
arch (presubmit_arch_darwin)	3m 57s
dashboard	2m 38s
arch (presubmit_arch_executor)	3m 18s
arch (presubmit_arch_linux)	10m 56s
arch (presubmit_arch_freebsd)	5m 58s
arch (presubmit_arch_openbsd)	3m 48s
	1h 12m 7s

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