CSS: Support omitting semicolon from last property

[chucker]

Description of Change

[ main may be the more appropriate branch, but it's a relatively small change. ]

The current CSS parser doesn't support declarations like label {font-size: 18; background-color: red} where the final semicolon is omitted. These are, however, valid CSS.

This fixes that behavior and introduces a few unit tests to check for such edge cases.

Issues Resolved

• fixes [Enhancement] Support minified stylesheets #2588

Testing Procedure

Run all tests in the Xamarin.Forms.Core.UnitTests.StyleSheets and Xamarin.Forms.StyleSheets.UnitTests namespaces.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[jfversluis]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jfversluis]

Hey @chucker thanks so much for your time and effort here and special thanks for your patience. Small change but I think some might be happy with it!