Auto indentation rules

C# indentation rules are missing from this extention so action based formatting will not work, see example below.

This has been brought up in a couple of other language extentions ([python](https://github.com/microsoft/vscode-python/issues/8996), [c++](https://github.com/microsoft/vscode-cpptools/issues/883)) and is a little niche but would be really cool to get this working in this extention as some other extentions rely on this method for formatting e.g. [VSCode/Vim](https://github.com/VSCodeVim/Vim)

## Steps to reproduce
Map a key to `editor.action.reindentselectedlines`
Put cursor inside a function on a line with an incorrectly line like this
Execute the key/action for `editor.action.reindentselectedlines`

## Expected behavior
The line should be formatted and indented correctly inside the function like this

## Actual behavior
The line remains in the same place as VSCode does not know the correctly indenting rules for the language