tools/clang/codesearch: migrate dyn_cast to dyn_cast_if_present #19153

Job	Run time
race	9m 39s
old	7m 42s
aux	4m 0s
gvisor	4m 3s
race_dashboard	3m 29s
build	3m 12s
dashboard	2m 50s
arch (presubmit_arch_darwin)	3m 25s
arch (presubmit_arch_windows)	3m 43s
arch (presubmit_arch_linux)	10m 43s
arch (presubmit_arch_executor)	3m 22s
arch (presubmit_arch_openbsd)	3m 48s
arch (presubmit_arch_netbsd)	4m 0s
arch (presubmit_arch_freebsd)	6m 31s
	1h 10m 27s

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