Remove TypeFieldMapper

[romseygeek]

We don't need a special TypeFieldMapper for anything in master; all access
to the type field can be done via a TypeFieldType that issues appropriate
deprecation warnings.

Relates to #41059

[elasticmachine]

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

[romseygeek]

@elasticmachine run elasticsearch-ci/1

[mayya-sharipova]

@romseygeek thanks, this PR LGTM. Just wanted to confirm with you that in 8.0 we still want to allow queries and aggs on _type field? Didn't we want to completely disallow this?

[romseygeek]

Didn't we want to completely disallow this?

Yes, we'll disallow it in a follow up but I wanted to get the deprecations into master and 7x first.

[romseygeek]

Hm, it looks like we can't actually backport this to 7x because the type field mapper is still used in various places, and the neat field type improvements don't work because the type itself is not necessarily known when then mapper is built. So we need to wait until 9x to remove things fully, unfortunately.