[DOCS] Field data types docs - Consistency improvements

[mattkime]

• [ ] Most of the numeric types are found at https://www.elastic.co/guide/en/elasticsearch/reference/current/number.html but unsigned long has its own page with some content not found on the number page - https://www.elastic.co/guide/en/elasticsearch/reference/current/unsigned-long.html
• [ ] murmur3 is shown along side built in types in https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-types.html but is available via a plugin. It should be called out in a separate section to make it more distinct. The same for mapper-annotated-text
• [x] completion is shown on https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-types.html but doesn't appear in the sidebar list of types on the same page.

related to https://github.com/elastic/kibana/issues/120289

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