pkg/codesearch: support finding field reads/writes #19136

Job	Run time
dashboard	1m 16s
old	1m 8s
aux	1m 4s
race	1m 17s
arch (presubmit_arch_openbsd)	1m 4s
race_dashboard	1m 16s
build	1m 18s
arch (presubmit_arch_windows)	1m 3s
arch (presubmit_arch_linux)	1m 4s
arch (presubmit_arch_darwin)	1m 3s
gvisor	1m 3s
arch (presubmit_arch_freebsd)	1m 4s
arch (presubmit_arch_executor)	1m 3s
arch (presubmit_arch_netbsd)	1m 4s
	15m 47s

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