Move analyzer resolution in mappings from parse to build

[romseygeek]

Analyzers are currently resolved in the parse phase, meaning that by the
time we build mappings we no longer have any references to IndexAnalyzers.
In future, we would like to move analysis resolution entirely into the build
phase, making it possible to construct catch-all text fields that are still
distinguished by analyzers. This commit is a first step, deferring analyzer
resolution in text-based fields to build and converting analyzer parameters
to be string-based.

[elasticsearchmachine]

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