feat: Allow disabling the icon background

[MartinZikmund]

Part of: #190

PR Type

What kind of change does this PR introduce?

• Feature

What is the current behavior?

Currently the user must create a new .svg file like icon_transparent.svg that is empty and provide it as the UnoIconBackgroundFile - as leaving this empty will fallback to icon.svg.

What is the new behavior?

New attribute allows setting UseIconBackground to false, which will not use the background file while generating, and will keep the foreground file only instead.

I made a follow up PR unoplatform/uno#17855 in Uno.UI to add a prop to control this and then default this to false on WASM, desktop and WinUI, where users most commonly don't want a background behind the icon.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Wasm UI Tests are not showing unexpected any differences. Validate PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Updated the Release Notes
• Associated with an issue (GitHub or internal)

Other information

Internal Issue (If applicable):

[MartinZikmund]

TODO docs, waiting for approval that this approach makes sense

[MartinZikmund]

@jeromelaban can you confirm this approach works?

[MartinZikmund]

This approach is compatible with #239

[jeromelaban]

Can you add a test with a validation for this part?

[nickrandolph]

@MartinZikmund I feel that an additional property is just highlighting an issue with the original implementation and I feel that we should be able to just use the two svg files provided. In my mind the foreground svg is the icon itself and on platforms that support a transparent background only this file would be used (if developer wants a background even on those platforms they can add this to the foreground svg). On platforms that don't support a transparent background, this is where the background svg would be used. Does this make sense, or are there scenarios I'm not thinking about