messages: Add JavaMethod and JavaStackTraceElement as SourceReference

Cucumber JVM can not reference files by URI. So it should use either java
methods or stack trace elements as a source reference instead.

For example:

```json
{
  "hook": {
    "id": "a1839ec6-f75d-4029-9b75-4b8203d8b2e8",
    "sourceReference": {
      "javaMethod": {
        "className": "io.cucumber.compatibility.attachments.Attachments",
        "methodName": "before",
        "methodParameterTypes": [
          "io.cucumber.java.Scenario"
        ]
      }
    }
  }
}
```

See: cucumber/cucumber-jvm#2058
Fixes: cucumber/common#1119

Author: mpkorstanje

messages.proto

@@ -137,10 +137,26 @@ message Location {
  * [Location](#io.cucumber.messages.Location) within that file.
  */
 message SourceReference {
-  string uri = 1;
+  oneof reference {
+    string uri = 1;
+    JavaMethod java_method = 3;
+    JavaStackTraceElement java_stack_trace_element = 4;
+  }
   Location location = 2;
 }
 
+message JavaMethod {
+  string class_name = 1;
+  string method_name = 2;
+  repeated string method_parameter_types = 3;
+}
+
+message JavaStackTraceElement {
+  string class_name = 1;
+  string method_name = 2;
+  string file_name = 3;
+}
+
 ////// Source
 
 /**