add .hx to MONO_EXTENSIONS

[VysotskiVadim]

Let's add .hx extension to supported extensions.
Haxe is language which can be compiled to c#, it overrides path and line number using line directive.

This Haxe code:

 public static function main() 
 {
        var array = 1...10;
        for (i in array){
            trace('Hello world $i');
        }
        
 }

will be compiled to this c# code:

public static void main() {
		unchecked {
			#line 5 "/Users/vadzimv/Projects/haxe_cs_debug/sample/Test.hx"
			global::IntIterator array = new global::IntIterator(1, 10);
			{
				#line 6 "/Users/vadzimv/Projects/haxe_cs_debug/sample/Test.hx"
				global::IntIterator _g = array;
				#line 6 "/Users/vadzimv/Projects/haxe_cs_debug/sample/Test.hx"
				while (( _g.min < _g.max )) {
					#line 6 "/Users/vadzimv/Projects/haxe_cs_debug/sample/Test.hx"
					int i = _g.min++;
					global::haxe.Log.trace.__hx_invoke2_o(default(double), global::haxe.lang.Runtime.concat("Hello world ", global::haxe.lang.Runtime.toString(i)), default(double), new global::haxe.lang.DynamicObject(new int[]{302979532, 1547539107, 1648581351}, new object[]{"main", "Test", "Test.hx"}, new int[]{1981972957}, new double[]{((double) (7) )}));
				}
				
			}
			
		}
		#line default
	}

Because of line directive mono debugger works well with .hx files, so I believe mono debugger can be used to debug haxe code for c# target without any other changes.

[weinand]

I would like to verify this. How do I compile Haxe to C# on macOS?

[VysotskiVadim]

Please install haxe: https://haxe.org/download/
I've published a simple project for you to test: https://github.com/VysotskiVadim/haxe-vscode-monodebug-sample , just open, put breakpoint and launch.

[weinand]

@VysotskiVadim thanks a lot for the PR and even more so for the sample project! That helped a lot.

[VysotskiVadim]

I'm glad to help! thanks.