Create preallocation utility functions for expressions

[MilesCranmer]

This creates allocate_container and copy_into! for preallocating storage for an expression or tree:

container = allocate_container(ex)

# The following code will result in zero allocations
for _ = 1:100
    ex2 = copy_into!(container, ex)
end

The allocate_container takes an n argument if you want to set a specific size. Otherwise it just takes it from ex.

[github-actions]

Pull Request Test Coverage Report for Build 12322510485

Details

• 70 of 70 (100.0%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 95.533%

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Totals
Change from base Build 12289055804:	0.2%
Covered Lines:	2545
Relevant Lines:	2664

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💛 - Coveralls

[github-actions]

Benchmark Results

	master	16c5ef0...	master/16c5ef08b12d27...
eval/ComplexF32/evaluation	7.23 ± 0.51 ms	7.24 ± 0.53 ms	0.999
eval/ComplexF64/evaluation	10.8 ± 0.83 ms	10.7 ± 0.86 ms	1.01
eval/Float32/derivative	12.5 ± 1.4 ms	11.6 ± 1.2 ms	1.07
eval/Float32/derivative_turbo	12.3 ± 1.6 ms	11.6 ± 1.3 ms	1.05
eval/Float32/evaluation	2.76 ± 0.24 ms	2.72 ± 0.25 ms	1.01
eval/Float32/evaluation_bumper	0.583 ± 0.014 ms	0.601 ± 0.013 ms	0.97
eval/Float32/evaluation_turbo	0.567 ± 0.031 ms	0.552 ± 0.034 ms	1.03
eval/Float32/evaluation_turbo_bumper	0.581 ± 0.014 ms	0.6 ± 0.013 ms	0.968
eval/Float64/derivative	16 ± 1.1 ms	15 ± 0.83 ms	1.06
eval/Float64/derivative_turbo	15.7 ± 1.1 ms	14.9 ± 0.71 ms	1.05
eval/Float64/evaluation	3.2 ± 0.3 ms	3.14 ± 0.32 ms	1.02
eval/Float64/evaluation_bumper	1.19 ± 0.043 ms	1.25 ± 0.044 ms	0.954
eval/Float64/evaluation_turbo	1.07 ± 0.068 ms	1.03 ± 0.068 ms	1.04
eval/Float64/evaluation_turbo_bumper	1.2 ± 0.042 ms	1.25 ± 0.045 ms	0.958
utils/combine_operators/break_sharing	0.0388 ± 0.00065 ms	0.0386 ± 0.00083 ms	1
utils/convert/break_sharing	27.9 ± 2.6 μs	27.2 ± 2.5 μs	1.02
utils/convert/preserve_sharing	0.0982 ± 0.0041 ms	0.099 ± 0.0044 ms	0.992
utils/copy/break_sharing	28.3 ± 2.5 μs	27.3 ± 2.3 μs	1.04
utils/copy/preserve_sharing	0.0992 ± 0.0039 ms	0.0985 ± 0.004 ms	1.01
utils/count_constant_nodes/break_sharing	8.87 ± 0.18 μs	8.81 ± 0.2 μs	1.01
utils/count_constant_nodes/preserve_sharing	0.0864 ± 0.0032 ms	0.0863 ± 0.0034 ms	1
utils/count_depth/break_sharing	9.66 ± 0.2 μs	9.68 ± 0.27 μs	0.999
utils/count_nodes/break_sharing	8.46 ± 0.18 μs	8.09 ± 0.22 μs	1.05
utils/count_nodes/preserve_sharing	0.087 ± 0.0032 ms	0.086 ± 0.0032 ms	1.01
utils/get_set_constants!/break_sharing	0.0336 ± 0.0022 ms	0.0332 ± 0.0021 ms	1.01
utils/get_set_constants!/preserve_sharing	0.178 ± 0.0056 ms	0.178 ± 0.0063 ms	1
utils/get_set_constants_parametric	0.0449 ± 0.0024 ms	0.0443 ± 0.0021 ms	1.01
utils/has_constants/break_sharing	4.1 ± 0.14 μs	4.07 ± 0.15 μs	1.01
utils/has_operators/break_sharing	1.97 ± 0.084 μs	2 ± 0.08 μs	0.986
utils/hash/break_sharing	23 ± 0.54 μs	22.7 ± 1.1 μs	1.01
utils/hash/preserve_sharing	0.0982 ± 0.0035 ms	0.0964 ± 0.0033 ms	1.02
utils/index_constant_nodes/break_sharing	25.4 ± 0.98 μs	25.3 ± 0.89 μs	1.01
utils/index_constant_nodes/preserve_sharing	0.0987 ± 0.0035 ms	0.0985 ± 0.0041 ms	1
utils/is_constant/break_sharing	4.45 ± 0.16 μs	4.42 ± 0.16 μs	1.01
utils/simplify_tree/break_sharing	0.187 ± 0.0037 ms	0.165 ± 0.0032 ms	1.13
utils/simplify_tree/preserve_sharing	0.233 ± 0.005 ms	0.216 ± 0.0047 ms	1.08
utils/string_tree/break_sharing	0.47 ± 0.017 ms	0.468 ± 0.019 ms	1
utils/string_tree/preserve_sharing	0.572 ± 0.021 ms	0.582 ± 0.025 ms	0.983
time_to_load	0.235 ± 0.0031 s	0.232 ± 0.011 s	1.01