Simplify function call syntax in attention.py and update `EncodeSource` to use `theta` argument, and update `LocationSensitiveAttention` to use the same names for its variables throughout the layer.
Simplify function call syntax in attention.py and update `EncodeSource` to use `theta` argument, and update `LocationSensitiveAttention` to use the same names for its variables throughout the layer.

Passing `theta` makes it clearer that an untransformed layer weight is being used and will simplify adding quantization.

PiperOrigin-RevId: 457106530

tensorflow/lingvo,tensorflow/lingvo,tensorflow/lingvo,tensorflow/lingvo