Adds conceptual docs for token graphs.
These docs cover:
* How a token graph is constructed from a token stream
* How synonyms and multi-position tokens impact token graphs
* How token graphs are used during search
* Why some token filters produce invalid token graphs
Also makes the following supporting changes:
* Adds anchors to the 'Anatomy of an Analyzer' docs for cross-linking
* Adds several SVGs for token graph diagrams
This helps the topic better match the structure of
our machine learning docs, e.g.
https://www.elastic.co/guide/en/machine-learning/7.5/ml-concepts.html
This PR only includes the 'Anatomy of an analyzer' page as a 'Concepts'
child page, but I plan to add other concepts, such as 'Index time vs.
search time', with later PRs.
* Docs: First pass at improving analyzer docs
I've rewritten the intro to analyzers plus the docs
for all analyzers to provide working examples.
I've also removed:
* analyzer aliases (see #18244)
* analyzer versions (see #18267)
* snowball analyzer (see #8690)
Next steps will be tokenizers, token filters, char filters
* Fixed two typos
James Rodewig
Achraf
Clinton Gormley