[Relay][CanonicalizeOps] Make Bias_add shape same as the other operand

[anijain2305]

Currently, the bias_add expansion is minimal, i.e., it expands the bias to the minimum number of dimensions and then rely on broadcast mechanism. This PR explicitly matches the dimension of bias_add to be exactly same as the other operand. This helps with the later stage in AlterOpLayout.

@icemelon9 @yzhliu @ZihengJiang

Alternative impl - Make AlterOpLayout flexible - #4040

[tqchen]

This is something that I am not sure about. I do think a better way would be to support general broadcast semantics, because users could reply on it instead of bias add

[anijain2305]

Yes, I agree. I don't like this either. This is restrictive only to bias_add. More concerning is that this is sort of leaky, creating dependency between two passes that are far apart. I will close this one.

The alternate one is more generic - #4040 and improves AlterOpLayout braodcast support.
It works for broadcast ops, instead of bias_add. It inserts expand_dims while transforming the layout.

[yzhliu]

I also prefer the one in #4040 and with that it seems we can directly remove this CanonicalizeOps pass.

[anijain2305]

Closing this. #4040 covers this.