Embedding sparsity optimization (#16141)
### Description
Optimize compute graph by eliminating padding in embedding.
### Motivation and Context
The computation for padding in nodes after embedding is unnecessary and
waste computation resources.
This pr just add an Optimizer of PaddingElimination to check and
eliminate the padding after embedding automatically by modifying the
graph.
### Implementation:
1. Find and check embedding node in graph.
2. Iterate the subgraph afterward the embedding node and record all the
input nodes and output nodes to this subgraph.
3. Insert 'Reshape + ShrunkenGather' to flatten each input node shape
from [batch_size, seqlen, ...] to [valid_token_without_padding, ...],
and insert 'GatherGrad + Reshape' to unflatten each output node shape
from [valid_token_without_padding, ...] to [batch_size, seqlen, ...]
---------
Co-authored-by: mindest <linminuser@gmail.com>
