Label encoder fusion (#19761)
### Description
Created a new `LabelEncoderFusion` pass. This is useful in model that
result from automatic conversion tools related to data-science:
sometimes the produced model contains consecutive `LabelEncoder`-s.
To merge 2 `LabelEncoder`-s the optimizer propagates the outputs of the
first encoder through the second one.
### Motivation and Context
This enhances the capabilities of the `onnxruntime::optimizer` by fusing
consecutive `LabelEncoder` nodes.
### Fusion examples
```
Applying fusion
node1: (a,C) (b,B) (c,A) -> Default: _Unused
node2: (A,1) (B,2) (C,3) -> Default: -1
fused: (a,3) (b,2) (c,1) -> Default: -1
Applying fusion
node1: (a,C) (b,B) (c,A) -> Default: D
node2: (A,a) (B,b) (C,c) (D,d) -> Default: default
fused: (a,c) (b,b) (c,a) -> Default: d
Applying fusion
node1: (a,0) (b,1) (c,2) -> Default: -1
node2: (2,a) (1,b) (0,c) -> Default: default
fused: (a,c) (b,b) (c,a) -> Default: default
Applying fusion
node1: (a,3) (b,2) (c,1) -> Default: -1
node2: (1,a) (2,b) (3,c) -> Default: d
fused: (a,c) (b,b) (c,a) -> Default: d
```
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Co-authored-by: Justin Chu <justinchuby@users.noreply.github.com>
