feat: add service invocation output variables

Author: Gregor Holzer

src/main/resources/pkl/csm/csml.pkl

@@ -99,6 +99,7 @@ class InvokeDescription extends ActionDescription {
   type: InvocationType
   mode: InvocationMode = "remote"
   input: Context
+  output: Listing<ContextVariableReferenceDescription>
   raises: Listing<EventDescription>
 }
 
@@ -122,10 +123,11 @@ class ResetDescription extends ActionDescription {
 
 class CaseDescription {
   of: Expression
-  then: Listing<ActionDescription>
+  then: ActionDescription
 }
 
 class MatchDescription extends ActionDescription {
+  value: Expression
   cases: Listing<CaseDescription>
   default: ActionDescription?
 }
@@ -134,6 +136,10 @@ class LogDescription extends ActionDescription {
   message: Expression
 }
 
+class ContextVariableReferenceDescription {
+  reference: String
+}
+
 typealias EventTopic = String(matches(Regex(#"^[a-zA-Z_]\w*$"#)))
 
 typealias EventChannel = "internal"|"external"|"global"|"peripheral"