Support for u0 initial guess function

[avik-pal]

Fixes #128

TODOs

• Upstream get_concrete_u0 patch so that u0 as a function is propagated unlike IVPs
• Add tests (use the one in Very long compilation time for solve() #117 (comment))

[avik-pal]

I will fix the piracy once SciML/DiffEqBase.jl#959 is merged and released.

[avik-pal]

I want to get this in before #131, since that one is major release.

[ChrisRackauckas]

note that in v1.10 this isn't needed, and it can be incorrect.

[github-actions]

Benchmark Results

	master	4740b04...	t[master]/t[4740b04...]
Simple Pendulum/IIP/MultipleShooting(10, Tsit5; grid_coarsening = false)	2.81 ± 0.1 ms	2.76 ± 0.073 ms	1.02
Simple Pendulum/IIP/MultipleShooting(10, Tsit5; grid_coarsening = true)	5.23 ± 0.19 ms	5.08 ± 0.12 ms	1.03
Simple Pendulum/IIP/MultipleShooting(100, Tsit5; grid_coarsening = false)	0.0737 ± 0.0056 s	0.0742 ± 0.0059 s	0.993
Simple Pendulum/IIP/MultipleShooting(100, Tsit5; grid_coarsening = true)	0.258 ± 0.0088 s	0.253 ± 0.0091 s	1.02
Simple Pendulum/IIP/Shooting(Tsit5())	0.251 ± 0.012 ms	0.244 ± 0.012 ms	1.03
Simple Pendulum/OOP/MultipleShooting(10, Tsit5; grid_coarsening = false)	7.14 ± 0.28 ms	7.12 ± 0.74 ms	1
Simple Pendulum/OOP/MultipleShooting(10, Tsit5; grid_coarsening = true)	12.8 ± 7.1 ms	13 ± 8.1 ms	0.984
Simple Pendulum/OOP/MultipleShooting(100, Tsit5; grid_coarsening = false)	0.195 ± 0.001 s	0.2 ± 0.0036 s	0.975
Simple Pendulum/OOP/MultipleShooting(100, Tsit5; grid_coarsening = true)	1.03 ± 0.018 s	1.03 ± 0.0088 s	1
Simple Pendulum/OOP/Shooting(Tsit5())	1.03 ± 0.095 ms	1.02 ± 0.12 ms	1.01
time_to_load	9.13 ± 0.14 s	8.81 ± 0.27 s	1.04

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).