add HeteroJK class

[m-atalla]

Hi,

this PR implements #9355, please do let me know if any additional changes or documentation is needed.
Thank you

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.86%. Comparing base (476e768) to head (3866ae5).

❗ Current head 3866ae5 differs from pull request most recent head 4d5ae36

Please upload reports for the commit 4d5ae36 to get more accurate results.

Files	Patch %	Lines
torch_geometric/nn/models/jumping_knowledge.py	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9380      +/-   ##
==========================================
- Coverage   87.99%   87.86%   -0.13%     
==========================================
  Files         473      473              
  Lines       30820    30830      +10     
==========================================
- Hits        27120    27090      -30     
- Misses       3700     3740      +40     

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