get_mesh_laplacian fix and normalization_type customization

[daniel-unyi-42]

Fixed get_mesh_laplacian, and user can select its normalization type (#6037)

[codecov]

Codecov Report

Merging #6790 (78e0751) into master (83d6f95) will decrease coverage by 0.09%.
The diff coverage is 90.24%.

❗ Current head 78e0751 differs from pull request most recent head f136463. Consider uploading reports for the commit f136463 to get more accurate results

@@            Coverage Diff             @@
##           master    #6790      +/-   ##
==========================================
- Coverage   91.44%   91.36%   -0.09%     
==========================================
  Files         425      425              
  Lines       22965    22971       +6     
==========================================
- Hits        21001    20987      -14     
- Misses       1964     1984      +20     

Impacted Files	Coverage Δ
torch_geometric/utils/get_mesh_laplacian.py	92.30% <90.24%> (-7.70%)	⬇️
torch_geometric/data/datapipes.py	60.34% <0.00%> (-13.80%)	⬇️
...ch_geometric/explain/algorithm/captum_explainer.py	88.88% <0.00%> (-11.12%)	⬇️
torch_geometric/explain/algorithm/captum.py	98.66% <0.00%> (-1.34%)	⬇️
torch_geometric/explain/algorithm/gnn_explainer.py	73.43% <0.00%> (-1.21%)	⬇️
torch_geometric/typing.py	100.00% <0.00%> (ø)
torch_geometric/loader/dataloader.py	100.00% <0.00%> (ø)

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