Support mutating functions f!(y, x)

[gdalle]

Core

• Define fallback structure for mutating functions f!(y, x)
• Add appropriate signatures to docstrings for value_and_pushforward!, value_and_pullback!, value_and_multiderivative!, value_and_jacobian!
• Add possible argument y to preparation functions
• Link most docstrings to function name instead of method

Extensions

• Put everyone into their own folder
• Fully support mutation with ForwardDiff
• Strengthen typing to resolve method ambiguities spotted by Aqua (whenever possible, type the storage but don't type the seed in case it's a Tangent / Thunk)

Docs

• Update README.md with the two kinds of functions: allocating and mutating
• Update docs/src/getting_started.md with an explanation of mutating functions
• Update docs/src/backends.md with the compatibility for mutating functions
• Update docs/src/developer.md with the fallback structure for mutating functions

Tests

• Add utilities to construct mutating Scenarios
• Insert mutating Scenarios into the default suite
• Toggle type stability wherever possible (jacobians are still unstable in a lot of places)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.55219% with 34 lines in your changes are missing coverage. Please review.

Project coverage is 91.14%. Comparing base (ccb7f43) to head (75eca1e).

Files	Patch %	Lines
...t/DifferentiationInterfaceTestExt/test_mutating.jl	69.72%	33 Missing ⚠️
...dDiffExt/DifferentiationInterfaceForwardDiffExt.jl	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
- Coverage   92.60%   91.14%   -1.46%     
==========================================
  Files          26       29       +3     
  Lines         649      881     +232     
==========================================
+ Hits          601      803     +202     
- Misses         48       78      +30     

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