feat: Add regexp_count function #33733

Job	Run time
cargo check	11m 5s
build with wasm-pack	2m 42s
cargo test (macos)	10m 52s
cargo test (macos-aarch64)	9m 42s
cargo test (win64)	1h 1m 44s
Check cargo fmt	42s
Verify MSRV (Min Supported Rust Version)	8m 10s
Verify Vendored Code	48s
cargo examples (amd64)	13m 28s
cargo test (amd64)	10m 39s
cargo doc	4m 2s
cargo test doc (amd64)	15m 47s
cargo test datafusion-cli (amd64)	4m 9s
cargo test pyarrow (amd64)	2m 52s
Run sqllogictest with Postgres runner	3m 34s
verify benchmark results (amd64)	12m 18s
check Cargo.toml formatting	3m 1s
clippy	5m 38s
check configs.md and ***_functions.md is up-to-date	3m 1s
cargo test hash collisions (amd64)	18m 10s
	3h 22m 24s

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