Turn get_rect_tx_log_ratio into associated function for TxSize #5256

Job	Run time
rustfmt-clippy	1m 36s
msrv	1m 25s
build-unix (beta-build)	2m 31s
wasi	51s
build-windows (cargo-build, x86_64-pc-windows-msvc)	3m 44s
build-unix (1.74.0-tests)	3m 52s
build-macos (Cargo build (x64), cargo-build, x86_64-apple-darwin)	1m 27s
build-unix (aom-tests)	4m 43s
build-windows (cargo-test, x86_64-pc-windows-msvc)	5m 57s
build-macos (Cargo test (x64), cargo-test, x86_64-apple-darwin)	1m 47s
build-windows (cargo-c, x86_64-pc-windows-gnu)	6m 57s
build-unix (dav1d-tests)	5m 15s
build-macos (Cargo C-build (x64), cargo-c, x86_64-apple-darwin)	3m 15s
build-unix (no-asm-tests)	7m 50s
build-macos (Cargo build (Arm64), cargo-build, aarch64-apple-darwin)	1m 20s
build-unix (grcov-codecov)	9m 30s
build-macos (Cargo C-build (Arm64), cargo-c, aarch64-apple-darwin)	2m 51s
build-unix (bench)	3m 46s
build-unix (doc)	2m 31s
build-unix (cargo-c)	4m 54s
build-unix (check-no-default)	1m 18s
build-unix (check-extra-feats)	2m 27s
build-unix (check-unstable-feats)	2m 23s
build-unix (fuzz)	5m 22s
build-unix (dav1d-tests-arm64, stable)	5m 51s
	1h 33m 23s

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