feat: allow separate operator names for pretty printing

[MilesCranmer]

This is part of the solution to MilesCranmer/PySR#843

Pointed out by @arcusfelis

The next stage is to assign different string representations for greater and related operators when in regular printing (used for saving to file) and pretty printing.

[coveralls]

Pull Request Test Coverage Report for Build 13595121827

Details

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 95.578%

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Files with Coverage Reduction	New Missed Lines	%
src/Strings.jl	1	93.41%

Totals
Change from base Build 13188501181:	-0.03%
Covered Lines:	2572
Relevant Lines:	2691

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💛 - Coveralls

[github-actions]

Benchmark Results

	master	e3cd937...	master / e3cd937...
eval/ComplexF32/evaluation	7.25 ± 0.6 ms	7.29 ± 0.63 ms	0.995
eval/ComplexF64/evaluation	10.8 ± 0.81 ms	10.9 ± 1.2 ms	0.992
eval/Float32/derivative	12 ± 1.1 ms	13.5 ± 2.3 ms	0.887
eval/Float32/derivative_turbo	12 ± 1.3 ms	13.1 ± 2.1 ms	0.918
eval/Float32/evaluation	2.74 ± 0.25 ms	2.79 ± 0.27 ms	0.982
eval/Float32/evaluation_bumper	0.608 ± 0.016 ms	0.59 ± 0.016 ms	1.03
eval/Float32/evaluation_turbo	0.556 ± 0.028 ms	0.609 ± 0.03 ms	0.914
eval/Float32/evaluation_turbo_bumper	0.609 ± 0.015 ms	0.587 ± 0.016 ms	1.04
eval/Float64/derivative	15 ± 0.83 ms	15.3 ± 0.73 ms	0.982
eval/Float64/derivative_turbo	15 ± 0.73 ms	15.8 ± 0.88 ms	0.947
eval/Float64/evaluation	3.17 ± 0.32 ms	3.21 ± 0.32 ms	0.989
eval/Float64/evaluation_bumper	1.26 ± 0.043 ms	1.2 ± 0.045 ms	1.05
eval/Float64/evaluation_turbo	1.05 ± 0.063 ms	1.11 ± 0.059 ms	0.944
eval/Float64/evaluation_turbo_bumper	1.25 ± 0.043 ms	1.19 ± 0.045 ms	1.05
utils/combine_operators/break_sharing	0.0384 ± 0.0005 ms	0.0386 ± 0.00078 ms	0.993
utils/convert/break_sharing	26.6 ± 3.2 μs	27.6 ± 3.1 μs	0.963
utils/convert/preserve_sharing	0.0984 ± 0.0062 ms	0.1 ± 0.0045 ms	0.983
utils/copy/break_sharing	26.9 ± 3.3 μs	28.7 ± 2.9 μs	0.938
utils/copy/preserve_sharing	0.0986 ± 0.0056 ms	0.0998 ± 0.0052 ms	0.988
utils/count_constant_nodes/break_sharing	9.06 ± 0.23 μs	8.37 ± 0.21 μs	1.08
utils/count_constant_nodes/preserve_sharing	0.0852 ± 0.0045 ms	0.0865 ± 0.0041 ms	0.986
utils/count_depth/break_sharing	9.59 ± 0.21 μs	9.96 ± 0.42 μs	0.964
utils/count_nodes/break_sharing	8.37 ± 0.18 μs	8.4 ± 0.23 μs	0.996
utils/count_nodes/preserve_sharing	0.0864 ± 0.0046 ms	0.0867 ± 0.0038 ms	0.997
utils/get_set_constants!/break_sharing	0.0332 ± 0.0029 ms	0.0336 ± 0.0024 ms	0.989
utils/get_set_constants!/preserve_sharing	0.179 ± 0.0086 ms	0.18 ± 0.0096 ms	0.997
utils/get_set_constants_parametric	0.0443 ± 0.0027 ms	0.0455 ± 0.0031 ms	0.973
utils/has_constants/break_sharing	4.14 ± 0.13 μs	4.3 ± 0.2 μs	0.962
utils/has_operators/break_sharing	1.98 ± 0.052 μs	2.21 ± 0.1 μs	0.896
utils/hash/break_sharing	22.7 ± 0.65 μs	23 ± 0.65 μs	0.987
utils/hash/preserve_sharing	0.0974 ± 0.005 ms	0.0991 ± 0.0047 ms	0.983
utils/index_constant_nodes/break_sharing	25.1 ± 1.5 μs	25.3 ± 1.3 μs	0.99
utils/index_constant_nodes/preserve_sharing	0.0987 ± 0.0046 ms	0.0986 ± 0.0046 ms	1
utils/is_constant/break_sharing	4.62 ± 0.13 μs	4.15 ± 0.18 μs	1.11
utils/simplify_tree/break_sharing	0.176 ± 0.0083 ms	0.174 ± 0.0075 ms	1.01
utils/simplify_tree/preserve_sharing	0.223 ± 0.0091 ms	0.222 ± 0.0092 ms	1
utils/string_tree/break_sharing	0.463 ± 0.017 ms	0.487 ± 0.023 ms	0.951
utils/string_tree/preserve_sharing	0.583 ± 0.032 ms	0.584 ± 0.025 ms	0.999
time_to_load	0.21 ± 0.0017 s	0.216 ± 0.0041 s	0.974