Move self_leq to the is_less_equal callable #2577

Job	Run time
externals (clang, x86, -msse2)	47m 14s
arm (clang, aarch64, -Wno-psabi)	31m 56s
externals (gcc, x86, -msse2)	52m 31s
arm (clang, arm, -Wno-psabi)	33m 22s
macosx (clang, x86_osx, -mavx)	1h 49m 54s
no_pch (clang, x86, -msse2)	57m 50s
no_pch (gcc, x86, -msse2)	59m 5s
nosimd (clang, x86, -DEVE_NO_SIMD)	39m 38s
nosimd (gcc, x86, -DEVE_NO_SIMD)	47m 4s
riscv (clang, riscv, -mrvv-vector-bits=128)	34m 38s
x86-clang (clang, x86, -msse4.2)	13m 50s
x86-clang (clang, x86, -mavx)	17m 15s
x86-clang (clang, x86, -mavx2)	16m 34s
other-arch (gcc, sve256, -Wno-psabi)	53m 34s
other-arch (gcc, sve512, -Wno-psabi)	1h 50m 33s
other-arch (gcc, ppc64, -Wno-psabi)	35m 23s
avx512 (clang, x86, -march=skylake-avx512)	37m 41s
avx512 (gcc, x86, -march=skylake-avx512)	50m 34s
other-cases (clang_libcpp, x86, -msse2)	23m 47s
other-cases (clang, x86, -mavx2 -mbmi2 -DEVE_USE_BMI_ON_AVX2)	27m 41s
other-cases (gcc, x86, -mavx2 -mbmi2 -DEVE_USE_BMI_ON_AVX2)	51m 39s
x86-gcc (gcc, x86, -msse4.2)	18m 2s
x86-gcc (gcc, x86, -mavx)	22m 13s
x86-gcc (gcc, x86, -mavx2)	21m 38s
	16h 53m 36s

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