Update syntax highlighting and fixed opaque text marking

[DamianSuess]

Feature includes:

• Added EditorConfig file to ensure Visual Studio settings match the project's unique preferences
• Updated syntax highlighting rules to match those in the latest ILSpy
• Added ILAsm-Mode-Dark.xshd style definition
• Added display setting, Highlight Current Line

[DamianSuess]

ha! silly me, just noticed the other ILSpy repo had an editorconfig. Replaced my implementation w/ the one you're using ;)

[DamianSuess]

Please let me know if there is anything else needed. Overall, I'd like to see a ThemeManager for the resource dictionaries so that the Dark/Light themes can be properly managed, thus unifying the projects a bit better. I figured that was a bit out of scope here without asking permission first.

[DamianSuess]

The latest check-in addresses an existing issue where the TextMarker's background box hides the selected text. The box is being drawn in TextMarkerService.Draw(..) on Line 118.

As a short workaround, I provided a semi-transparent color. Considering that the same code is being used for the WPF TextMarkerService and even the sample project, I'm guessing this may be an issue w/ AvaloniaEdit?

[DamianSuess]

Lastly, here is a sample screenshot of the improved text selection and text marking

Before:

After:

[DamianSuess]

Any thoughts on this PR?
Let me know of any suggested changes