Add RTL support based on decorations

[remcohaszing]

This adds RTL support to Monaco editor. A line can be marked as RTL using decorations. Decorations can now specify a text direction. For every line, the decorations on that line are counted which specify the text direction. If there are more RTL decorations than there are RTL decorations, the line is considered RTL.

If a line is RTL, the content is aligned to the right side of the screen, taking the scrollbar into account.

If text content matches the text direction, pressing a left or right arrow key, moves the cursor into the same direction. If the content is of the inverse direction, the cursor is moved into the opposite direction.

The Home key moves the cursor to the start of the line. In case of RTL, this is the right.

The End key moves the cursor to the end of the line. In case of RTL, this is the left.

These cursor movements also work for multi selections.

Both RTL and LTR work with or without text wrapping, even with the advanced text wrapping strategy.

[remcohaszing]

I forgot to mention a couple of details.

1. Adding a decoration with textDirection, does not trigger a rerender yet. For my testing I used a decoration with an additional inlineClassName.
2. This change only affects Monaco editor yet. There should be an option for VSCode as well.
3. I’ve also thought about detecting RTL content. I don’t think it can be done. The meaning of a line in plain text really depends on context, e.g. the programming language. Also people have different preferences. I think this is best left to third party extensions.
4. This PR fixes a number of open issues.

I see you’re making some changes to my PR. Let me know if you need more info or I can help otherwise.

[alexdima]

Thank you!