Move modals to a separate component and replace markdown in locales with HTML

[obulat]

Fixes

Fixes #279 by @obulat

Description

Currently, the Modals for the Help section in the Chooser are converted from markdown in the locales.json files to HTML using markdown-it package at runtime. This PR replaces markdown with HTML to improve bundle size. Modals are also moved to a separate component to improve code organization.

Technical details

This PR extracts help modals from the HelpSection component into a separate ChooserModal component.

Previously, we have introduced vue-simple-portal package to render the modals in a separate div at the end of the body to fix a rendering problem: without the portal, you could see the underlying text through the modal. With the introduction of AppModal component from Vue Vocabulary, this problem was solved, so this PR removes vue-simple-portal package.

This PR also removes markdown from the modals, replacing them with HTML instead.
These changes make the un-compressed chunk-vendors 100 KiB smaller:

File                                   Size                        Gzipped
Before:
dist\js\chunk-vendors.f5ee90ab.js    388.52 KiB                  126.59 KiB
After:
dist\js\chunk-vendors.32fb3bc7.js    286.91 KiB                   89.75 KiB

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main or master).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[zackkrida]

Great to see the frontend bundle size reduction 👏