[JS] Take into account all the required fields for some computations

- Fix Field::getArray in order to collect only the fields which have a value;
- Fix AFSimple_Calculate:
  * allow to have a string with a list of field names as argument;
  * since a field can be non-terminal, use Field::getArray to collect
    the field under it and then apply the calculation on all the descendants.

src/scripting_api/aform.js

@@ -500,14 +500,18 @@ class AForm {
 
     const event = globalThis.event;
     const values = [];
+
+    cFields = this.AFMakeArrayFromList(cFields);
     for (const cField of cFields) {
       const field = this._document.getField(cField);
       if (!field) {
         continue;
       }
-      const number = this.AFMakeNumber(field.value);
-      if (number !== null) {
-        values.push(number);
+      for (const child of field.getArray()) {
+        const number = this.AFMakeNumber(child.value);
+        if (number !== null) {
+          values.push(number);
+        }
       }
     }