Add `AVInputFomat::find`, make `AVFormatContextInput::open` accept format hint #319

Job	Run time
rust_clippy_check_ubuntu	7m 47s
docs_rs_check	59s
build_dynamic_and_test_windows_pre	9m 43s
build_static_and_test_ubuntu (release/4.3, nightly, no valgrind)	9m 1s
build_static_and_test_ubuntu (release/4.3, 1.64.0, no valgrind)	11m 14s
build_static_and_test_ubuntu (release/5.0, nightly, no valgrind)	13m 2s
build_static_and_test_ubuntu (release/5.0, 1.64.0, no valgrind)	10m 23s
build_static_and_test_ubuntu (release/6.0, nightly, valgrind)	1h 57m 46s
build_static_and_test_ubuntu (release/6.0, nightly, no valgrind)	9m 16s
build_static_and_test_ubuntu (release/6.0, 1.64.0, no valgrind)	13m 7s
rust_clippy_check_windows	2m 31s
rustfmt_check (macos-latest)	39s
rustfmt_check (windows-latest)	41s
rustfmt_check (ubuntu-latest)	7s
build_dynamic_and_test_windows (nightly)	3m 5s
build_dynamic_and_test_windows (1.64.0)	3m 48s
	3h 33m 9s

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