Implement `get_keys` function in fts (#4647) #14556

Job	Run time
python lint check	23s
rustfmt check	11s
sanity checks	11s
clang format	36s
rust build & test	13m 47s
clang tidy & clangd diagnostics check	22m 21s
shell test	13m 2s
generate binary dataset	1m 28s
code coverage	31m 58s
gcc build & test	13m 49s
webassembly build & test	15m 18s
clang build & test	13m 28s
apple clang build & test	9m 8s
msvc build & test	33m 49s
macos extension test	2m 10s
clang build & test with page_size_log2=16	14m 48s
clang build & test with page_size_log2=18	15m 2s
gcc build & test with asan	38m 32s
gcc build & test in-mem only with various vector size	3m 16s
linux extension test	3m 9s
benchmark / benchmark	15m 13s
report benchmark result	0s
windows extension test	7m 49s
	4h 29m 28s

Provide feedback