chore: add kotlin code splitter (#11364)

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- **Description:** Adds Kotlin language to `TextSplitter`

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

docs/snippets/modules/data_connection/document_transformers/text_splitters/code_splitter.mdx

@@ -17,6 +17,7 @@ from langchain.text_splitter import (
     ['cpp',
      'go',
      'java',
+     'kotlin',
      'js',
      'ts',
      'php',