ColorPicker Simple Theme Fixes

[robloo]

What does the pull request do?

Fixes a few issues with the ColorView and ColorPicker in simple theme. I was always hoping simple theme was going away so the initial theme was only functional. This fixes a few issues though which is important now that it's used in dev tools and things.

What is the current behavior?

1. You have to click the tab icon to change tabs. Instead, anywhere should be allowed
2. The padding in the hex color input TextBox is bad
3. NumericUpDown shows a vertical scrollbar when it shouldn't

What is the updated/expected behavior with this PR?

1. You have to click the tab icon to change tabs. Instead, anywhere should be allowed
   • This is really an issue with the TabControl theme but I'm not fixing it there to avoid breaking other code. I'm just adding a transparent background in the color picker templates instead.
2. The padding in the hex color input TextBox is bad
   • This is really an issue with the underlying TextBox IMO but I'm not fixing it generically as it would be breaking. Instead, I'm just copying the better padding from the Fluent theme to use here. The Fluent theme is designed for 32px height controls already.
3. NumericUpDown shows a vertical scrollbar when it shouldn't
   • Again, this is an issue of TextBox in the simple theme. I didn't feel like addressing the issue there. However, it was fixed for all NumericUpDown controls. These controls should always be one line so don't require vertical scrolling. Therefore, vertical scrolling was just disabled across the board for this control.

How was the solution implemented (if it's not obvious)?

As described above.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

None

Obsoletions / Deprecations

None

Fixed issues

Fixes #16497

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0051151-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[robloo]

@cla-avalonia agree

[maxkatz6]

LGTM, thank you.

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0051257-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]