Add option to set html

[exeldro]

Description

Add option to set html instead of url or local file

Motivation and Context

Want to be able to display html and control the contents from plugins and scripts without having to host a file. When changing the css or html the browser only changes that part instead of destroying and creating a new browser.

How Has This Been Tested?

On windows11 by setting html as shown in above screenshot

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.

[exeldro]

I got the same effect working with some javascript events in this plugin: https://github.com/exeldro/obs-markdown So this PR is not needed for me any more