Try to normalize family names for embedded fonts

[Gillibald]

• Allow loading typefaces with a family name that includes known keywords like Bold, Black, etc.
• Make sure we filter out null family names when we call SKFontManager.GetInstalledFontFamilyNames
• Normalize family names specified via fontSource#FamilyName so known keywords are filtered out before caching them in the font collection.

What does the pull request do?

What is the current behavior?

What is the updated/expected behavior with this PR?

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

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

Obsoletions / Deprecations

Fixed issues

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0048372-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[Gillibald]

@cla-avalonia agree

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0048566-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]