fix: correct spelling mistakes of "seperate, intialise, pre-defined" (#14647)

fix spellings

**seperate -> separate**: found more occurrences, see
https://github.com/langchain-ai/langchain/pull/14602
**initialise -> intialize**: the latter is more common in the repo
**pre-defined > predefined**: adding a comma after a prefix is a
delicate matter, but this is a generally accepted word

also, another word that appears in the repo is "fs" (stands for
filesystem), e.g., in `libs/core/langchain_core/prompts/loading.py`
` """Unified method for loading a prompt from LangChainHub or local
fs."""`
Isn't "filesystem" better?

libs/community/langchain_community/vectorstores/semadb.py

@@ -36,7 +36,7 @@ class SemaDB(VectorStore):
         distance_strategy: DistanceStrategy = DistanceStrategy.EUCLIDEAN_DISTANCE,
         api_key: str = "",
     ):
-        """Initialise the SemaDB vector store."""
+        """initialize the SemaDB vector store."""
         self.collection_name = collection_name
         self.vector_size = vector_size
         self.api_key = api_key or get_from_env("api_key", "SEMADB_API_KEY")