build: fix typing/mypy issues

tensorflow-stubs/keras/layers/experimental/__init__.pyi

@@ -0,0 +1,4 @@
+from keras.api._v2.keras.layers.experimental import preprocessing as preprocessing
+from keras.layers.core.einsum_dense import EinsumDense as EinsumDense
+from keras.layers.kernelized import RandomFourierFeatures as RandomFourierFeatures
+from keras.layers.normalization.batch_normalization import SyncBatchNormalization as SyncBatchNormalization

tensorflow-stubs/keras/layers/experimental/preprocessing/__init__.pyi

@@ -0,0 +1,10 @@
+from keras.engine.base_preprocessing_layer import PreprocessingLayer as PreprocessingLayer
+from keras.layers.preprocessing.category_encoding import CategoryEncoding as CategoryEncoding
+from keras.layers.preprocessing.discretization import Discretization as Discretization
+from keras.layers.preprocessing.hashed_crossing import HashedCrossing as HashedCrossing
+from keras.layers.preprocessing.hashing import Hashing as Hashing
+from keras.layers.preprocessing.image_preprocessing import CenterCrop as CenterCrop, RandomContrast as RandomContrast, RandomCrop as RandomCrop, RandomFlip as RandomFlip, RandomHeight as RandomHeight, RandomRotation as RandomRotation, RandomTranslation as RandomTranslation, RandomWidth as RandomWidth, RandomZoom as RandomZoom, Rescaling as Rescaling, Resizing as Resizing
+from keras.layers.preprocessing.integer_lookup import IntegerLookup as IntegerLookup
+from keras.layers.preprocessing.normalization import Normalization as Normalization
+from keras.layers.preprocessing.string_lookup import StringLookup as StringLookup
+from keras.layers.preprocessing.text_vectorization import TextVectorization as TextVectorization