Themeable ItemCollectionMapperComponent and CollectionItemMapperComponent

[jensvannerum]

Description

This PR makes the ItemCollectionMapperComponent and CollectionItemMapperComponent themeable by default,

Instructions for Reviewers

Enable the "custom" theme and for both components, make some modifications to the component in the custom theme that are obvious.

The ItemCollectionMapperComponent is visible at: Edit Item -> Collection Mapper
The CollectionItemMapperComponent is visible at: Edit Collection -> Item Mapper

Include guidance for how to test or review your PR. This may include: steps to reproduce a bug, screenshots or description of a new feature, or reasons behind specific changes.

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes ESLint validation using npm run lint
• My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• My PR aligns with Accessibility guidelines if it makes changes to the user interface.
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• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.

[github-actions]

Hi @jensvannerum,
Conflicts have been detected against the base branch.
Please resolve these conflicts as soon as you can. Thanks!