Implement `float_to_int()` function #73

Job	Run time
test (ubuntu-latest, stable)	31s
cross-compile (ubuntu-latest, 1.70.0, aarch64-linux-android)	32s
cross-compile (ubuntu-latest, 1.70.0, i686-pc-windows-gnu)	34s
test (ubuntu-latest, beta)	28s
cross-compile-ios (macos-latest, 1.70.0, aarch64-apple-ios)	32s
cross-compile (ubuntu-latest, 1.70.0, i686-unknown-freebsd)	31s
test (ubuntu-latest, nightly)	30s
cross-compile (ubuntu-latest, 1.70.0, i686-unknown-linux-gnu)	37s
test (macos-latest, stable)	34s
cross-compile (ubuntu-latest, 1.70.0, wasm32-unknown-unknown)	30s
test (macos-latest, beta)	32s
cross-compile (ubuntu-latest, 1.70.0, x86_64-apple-darwin)	34s
test (macos-latest, nightly)	46s
cross-compile (ubuntu-latest, 1.70.0, x86_64-unknown-redox)	29s
test (windows-latest, stable)	2m 30s
test (windows-latest, beta)	1m 39s
test (windows-latest, nightly)	1m 31s
	13m 20s

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