Add TF-free impls of SentencePieceTokenizer, BytePairTokenizer, StartEndPacker and MultiSegmentPacker (#2557)

* TF-text free version of `SentencePieceTokenizer`, `BytePairTokenizer`, `StartEndPacker`, `MultiSegmentPacker` and `CausalLMPreprocessor`.

* Fix formatting.

* Address gemini-code-assist comments.

* Address Gemini's comments.

* Address Gemini's comments.

* Address Gemini's comments.

Author: james77777778

keras_hub/api/layers/__init__.py

@@ -4,6 +4,7 @@
 since your modifications would be overwritten.
 """
 
+from keras_hub.layers import v2 as v2
 from keras_hub.src.layers.modeling.alibi_bias import AlibiBias as AlibiBias
 from keras_hub.src.layers.modeling.anchor_generator import (
     AnchorGenerator as AnchorGenerator,

keras_hub/api/layers/v2/__init__.py

@@ -0,0 +1,12 @@
+"""DO NOT EDIT.
+
+This file was autogenerated. Do not edit it by hand,
+since your modifications would be overwritten.
+"""
+
+from keras_hub.src.layers.preprocessing.v2.multi_segment_packer import (
+    MultiSegmentPacker as MultiSegmentPacker,
+)
+from keras_hub.src.layers.preprocessing.v2.start_end_packer import (
+    StartEndPacker as StartEndPacker,
+)

keras_hub/api/models/__init__.py

@@ -4,6 +4,7 @@
 since your modifications would be overwritten.
 """
 
+from keras_hub.models import v2 as v2
 from keras_hub.src.models.albert.albert_backbone import (
     AlbertBackbone as AlbertBackbone,
 )

keras_hub/api/models/v2/__init__.py

@@ -0,0 +1,9 @@
+"""DO NOT EDIT.
+
+This file was autogenerated. Do not edit it by hand,
+since your modifications would be overwritten.
+"""
+
+from keras_hub.src.models.v2.causal_lm_preprocessor import (
+    CausalLMPreprocessor as CausalLMPreprocessor,
+)

keras_hub/api/tokenizers/__init__.py

@@ -146,3 +146,4 @@
 from keras_hub.src.tokenizers.word_piece_tokenizer_trainer import (
     compute_word_piece_vocabulary as compute_word_piece_vocabulary,
 )
+from keras_hub.tokenizers import v2 as v2

keras_hub/api/tokenizers/v2/__init__.py

@@ -0,0 +1,12 @@
+"""DO NOT EDIT.
+
+This file was autogenerated. Do not edit it by hand,
+since your modifications would be overwritten.
+"""
+
+from keras_hub.src.tokenizers.v2.byte_pair_tokenizer import (
+    BytePairTokenizer as BytePairTokenizer,
+)
+from keras_hub.src.tokenizers.v2.sentence_piece_tokenizer import (
+    SentencePieceTokenizer as SentencePieceTokenizer,
+)