Added support for heterogeneous graphs in AttentionExplainer

[XinweiHe]

Fixes #9112

[wsad1]

Nice work.
Can we test for HGTConv and HanConv, to ensure that it works for Hetero GNNs not created by the to_hetero operation.

[XinweiHe]

Can we test for HGTConv and HanConv, to ensure that it works for Hetero GNNs not created by the to_hetero operation.

HGTConv and HanConv are not relevant here, because AttentionExplainer only works with GNN model with attentions, in particular, GATConv, GATv2Conv or TransformerConv.

We will support HeteroConv with these attention GNN models in this PR though.

[codecov]

Codecov Report

Attention: Patch coverage is 89.13043% with 10 lines in your changes missing coverage. Please review.

Please upload report for BASE (xinwei_support_pg_explainer_hetero_v3@744f830). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...geometric/explain/algorithm/attention_explainer.py	89.13%	10 Missing ⚠️

Additional details and impacted files

@@                           Coverage Diff                            @@
##             xinwei_support_pg_explainer_hetero_v3   #10169   +/-   ##
========================================================================
  Coverage                                         ?   85.36%           
========================================================================
  Files                                            ?      496           
  Lines                                            ?    33840           
  Branches                                         ?        0           
========================================================================
  Hits                                             ?    28889           
  Misses                                           ?     4951           
  Partials                                         ?        0           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[wsad1]

HGTConv and HanConv are not relevant here, because AttentionExplainer only works with GNN model with attentions, in particular, GATConv, GATv2Conv or TransformerConv.

HanConv and HGTConv use attention while message passing.

[XinweiHe]

HanConv and HGTConv use attention while message passing.

You are right but at the moment, attention explainer is only designed to handle the case where alpha exists as an input parameter in def message(...) function. Since this is not the setup for HanConv and HGTConv at the moment we would need to spend extra effort supporting them which would probably be the best to not mix with this initial heterogeneous graph support for attention explainer.

[XinweiHe]

could we get this effort merge and create a follow-up ticket to handle the HanConv and HGTConv cases?

[wsad1]

Looks good.
Lets have a quick follow up for HANConv and other hetro GNNs.