feat(card-template-editor): introduce FieldFilters [DEV-only]

[david-allison]

Note

Assisted-by: Claude Opus 4.6
Discussed design, most of the code was mine
The concept of canApplyTo/updateContext was the largest contribution

Purpose / Description

See #20533 for context

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)

Fixes

• Issue Expose 'Field filters' in 'Insert field' #20533

Approach

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

How Has This Been Tested?

Unit tested

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[mikehardy]

Let's go