Adds conceptual documentation for stemming, including:
* An overview of why stemming is helpful in search
* Algorithmic vs. dictionary stemming
* Token filters used to control stemming, such as `stemmer_override`, `keyword_marker`, and `conditional`
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
* [DOCS] Rewrite analysis intro. Move index/search analysis content.
* Rewrites 'Text analysis' page intro as high-level definition.
Adds guidance on when users should configure text analysis
* Rewrites and splits index/search analysis content:
* Conceptual content -> 'Index and search analysis' under 'Concepts'
* Task-based content -> 'Specify an analyzer' under 'Configure...'
* Adds detailed examples for when to use the same index/search analyzer
and when not.
* Adds new example snippets for specifying search analyzers
* clarifications
* Add toc. Decrement headings.
* Reword 'When to configure' section
* Remove sentence from tip
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.
James Rodewig