Support 5/1-bit encoded TGA images. #1519

Job	Run time
Fuzz targets (cargo-fuzz)	54s
cargo-deny	18s
Fuzz targets (afl)	2m 3s
build_benchmarks	44s
cargo-semver-checks	27s
clippy	2m 6s
public_private_dependencies	24s
rustfmt	6s
test_avif_decoding	1m 17s
test_features	32s
test_other_archs (powerpc-unknown-linux-gnu)	2m 14s
test_features (default)	1m 47s
test_other_archs (i686-unknown-linux-gnu)	1m 16s
test_toolchains (1.67.1)	36s
test_features (rayon)	30s
test_toolchains (nightly)	1m 13s
test_features (avif)	56s
test_toolchains (beta)	1m 22s
test_features (bmp)	24s
test_features (dds)	23s
test_features (exr)	35s
test_features (ff)	36s
test_features (gif)	29s
test_features (hdr)	28s
test_features (ico)	35s
test_features (jpeg)	29s
test_features (png)	27s
test_features (pnm)	27s
test_features (qoi)	27s
test_features (tga)	27s
test_features (tiff)	30s
test_features (webp)	23s
	25m 25s

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