Replace MatrixDirichlet and TensorDirichlet with DirichletCollection

[wouterwln]

This pull request primarily focuses on renaming the TensorDirichlet distribution to DirichletCollection and updating all related references and functionality across various files. We also delete MatrixDirichlet. The most important changes include updating the benchmark files, documentation, and source code to reflect this renaming.

Renaming and updates:

• benchmark/benchmarks.jl: Updated the include statement to reference dirichlet_collection.jl instead of tensordirichlet.jl.
• benchmark/benchmarks/dirichlet_collection.jl: Added new benchmark groups and tests for the DirichletCollection distribution.
• docs/src/library.md: Replaced references to TensorDirichlet with DirichletCollection in the documentation. [1] [2]
• src/ExponentialFamily.jl: Updated include statements to reference dirichlet_collection.jl instead of tensor_dirichlet.jl. [1] [2]
• src/distributions/dirichlet_collection.jl: Renamed from tensor_dirichlet.jl and updated all internal references and functionality to use DirichletCollection. [1] [2] [3] [4] [5] [6] [7] [8] [9]

[codecov]

Codecov Report

Attention: Patch coverage is 93.54839% with 4 lines in your changes missing coverage. Please review.

Project coverage is 81.50%. Comparing base (3e91e64) to head (47606c4).

Files with missing lines	Patch %	Lines
src/distributions/dirichlet_collection.jl	92.72%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #229      +/-   ##
==========================================
- Coverage   81.77%   81.50%   -0.28%     
==========================================
  Files          41       40       -1     
  Lines        3478     3373     -105     
==========================================
- Hits         2844     2749      -95     
+ Misses        634      624      -10     

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