feat(card-template-editor): introduce FieldFilters

FieldFilters are the filters to the left side of a Field: {{type:Front}}

Users should be made aware of all available filters.

We first introduce the concept, then the concept of a chain:
{{kana:text:Front}}.

Due to various capabilities of a chain, some filters may not be applied
on top of others (`tts` is terminal; text removes HTML; hint adds HTML)

So we define validation rules on top of a chain based on 'context':
 `canApplyTo` and `updateContext` over a `FilterContext`

This allows UI validation: "once a user has applied `hint`, no
 longer allow them to apply `text`"

FieldFilters contains the object, we use 'ALL' as the filters inherit
 from `FieldFilter`, not `FieldFilters`

Issue 20533

Assisted-by: Claude Opus 4.6

Author: david-allison