Consider merging word_delimiter and word_delimiter_graph

[romseygeek]

We have an open PR (#29216) deprecating word_delimiter filter in favour of word_delimiter_graph filter. Similarly, we also have synonym and synonym_graph filter, the first of which ought to be deprecated in favour of the second.

The difference in both of these cases between the deprecated and non-deprecated versions is that the _graph filters correctly assign position lengths to their output, creating properly-formed graphs. However, as lucene does not store position lengths in the index, this makes no difference at index time, only at query time. For this reason (and because I don't think anybody intentionally wants a badly-formed query), maybe we should simply map both forms to the _graph implementation under the hood? This would also save having to re-index when upgrading with mappings that use word_delimiter or synonym.

[elasticmachine]

Pinging @elastic/es-search

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)