Fix Dropout Implementation in Graphormer (#24817)
This commit corrects the dropout implementation in Graphormer, aligning it with the original implementation and improving performance. Specifically:
1. The `attention_dropout` variable, intended for use in GraphormerMultiheadAttention, was defined but not used. This has been corrected to use `attention_dropout` instead of the regular `dropout`.
2. The `activation_dropout` for the activations in the feed-forward layers was missing. Instead, the regular `dropout` was used. This commit adds `activation_dropout` to the feed-forward layers.
These changes ensure the dropout implementation matches the original Graphormer and delivers empirically better performance.
