Add 'git survey' builtin using path-walk API #1896

Job	Run time
config	4s
fuzz smoke test	35s
win+VS build	0s
win build	2m 46s
documentation	3m 36s
linux32 (daald/ubuntu32:xenial)	1m 40s
linux-musl (alpine)	7m 13s
pedantic (fedora)	1m 42s
sparse	3m 19s
win+VS test	0s
static-analysis	3m 55s
linux-asan-ubsan (ubuntu-latest)	31m 1s
linux-gcc (ubuntu-20.04)	9m 51s
linux-gcc-default (ubuntu-latest)	10m 16s
linux-leaks (ubuntu-latest)	15m 27s
linux-reftable (ubuntu-latest)	10m 25s
linux-reftable-leaks (ubuntu-latest)	16m 38s
linux-sha256 (ubuntu-latest)	10m 9s
linux-TEST-vars (ubuntu-20.04)	10m 7s
osx-clang (macos-13)	19m 38s
osx-gcc (macos-13)	36m 53s
osx-reftable (macos-13)	12m 23s
win test	0s
	3h 27m 38s

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