[ES|QL] Add CHUNK function

[kderusso]

Adds a new function, CHUNK that takes text from a field and returns chunks based on the requested chunking strategy.

For this PR, we're inputting a size which will correspond to the default number of words in a sentence based chunking strategy. Future planned PRs will include the support for explicit chunking settings or an inference ID on top of these defaults. Future optimizations could also include supporting a max chunk size of LIMIT and optimizations to semantic text fields.

Examples of how to call this function:

FROM wikipedia
 | WHERE MATCH(content, \"churchill\") 
 | EVAL chunks = chunk(content, 3, 20) 
 | MV_EXPAND chunks
 | KEEP chunks
 | LIMIT 10

FROM wikipedia
 | WHERE MATCH(content, \"churchill\") 
 | EVAL chunks = chunk(content, 3) 
 | MV_EXPAND chunks
 | KEEP chunks
 | LIMIT 10 

FROM wikipedia
 | WHERE MATCH(content, \"churchill\") 
 | EVAL chunks = chunk(content) 
 | MV_EXPAND chunks
 | KEEP chunks
 | LIMIT 10