make dubCompiler setting machine-specific

For remote development this means the compiler must be changed on the
remote machine and won't be inherited from user settings.

However workspace / folder settings are unaffected and will still work.

This change is because dubCompiler is very platform specific and can
include full local paths.

Sync extensions might also respect this.

Author: WebFreak001

package.json

@@ -539,7 +539,7 @@
 				},
 				"d.dubCompiler": {
 					"type": "string",
-					"scope": "resource",
+					"scope": "machine-overridable",
 					"description": "Sets the default compiler to use when starting up"
 				},
 				"d.overrideDfmtEditorconfig": {