Fix Mixin breakpoints no longer working

Gradle run configs like FG3 mods ones do not execute the extension's
 #attachToProcess method, thus preventing MixinPositionManagerFactory
 from creating the PositionManager for the debugged process

The easiest solution is to simply remove the need for the extension
 and always return a MixinPositionManager.
 I do not think this can cause any issue, and the Groovy plugin does
 that for instance

Author: RedNesto

src/main/kotlin/com/demonwav/mcdev/platform/mixin/debug/MixinDebug.kt

@@ -16,11 +16,5 @@ import com.intellij.debugger.engine.DebugProcess
 
 class MixinPositionManagerFactory : PositionManagerFactory() {
 
-    override fun createPositionManager(process: DebugProcess): PositionManager? {
-        return if (process.processHandler.hasMixinDebugKey()) {
-            MixinPositionManager(process)
-        } else {
-            null
-        }
-    }
+    override fun createPositionManager(process: DebugProcess): PositionManager? = MixinPositionManager(process)
 }

src/main/kotlin/com/demonwav/mcdev/platform/mixin/debug/MixinPositionManagerFactory.kt

@@ -268,7 +268,6 @@
 
         <customJavadocTagProvider implementation="com.demonwav.mcdev.platform.mixin.MixinCustomJavaDocTagProvider"/>
 
-        <runConfigurationExtension implementation="com.demonwav.mcdev.platform.mixin.debug.MixinRunConfigurationExtension"/>
         <debugger.positionManagerFactory implementation="com.demonwav.mcdev.platform.mixin.debug.MixinPositionManagerFactory"/>
         <debuggerClassFilterProvider implementation="com.demonwav.mcdev.platform.mixin.debug.MixinDebuggerClassFilterProvider"/>