Integrate alphaSkia

[Danielku15]

Issues

Fixes #1222

Proposed changes

• Drop SkiaSharp and Skija in favor of our own new alphaSkia wrapper.
• Web Tests: Replaced Karma+Chrome with Node+alphaSkia+Test Result Viewer
• Replaced TSLint with ESLint
• Updated many dependencies to the latest version
• Modernized the Kotlin project
• Kotlin and C# Transpiler: Improved async code support (might allow an async API surface for alphaTab at some point)

Checklist

• I consent that this change becomes part of alphaTab under it's current or any future open source license
• Changes are implemented
• Existing builds tests pass
• New tests were added

Further details

• This is a breaking change
• This change will require update of the documentation/website