Fixing bug where an error is displayed when saving a new scripted fie…

…ld (#10820)

* Fixing bug where an error is displayed when saving a new scripted field

When a new scripted field is saved, there is a moment where a mapping
error validation message is displayed because there's a field with the
same name. Added a `saving` flag that is used to no longer show the
validation message in this situation.

* Switching approach to copying fieldNames on instantiation

src/ui/public/field_editor/field_editor.html

@@ -16,7 +16,7 @@
       class="form-control"
       data-test-subj="editorFieldName">
   </div>
-  <div ng-if="editor.creating && editor.indexPattern.fields.byName[editor.field.name]" class="hintbox">
+  <div ng-if="editor.creating && editor.existingFieldNames.includes(editor.field.name)" class="hintbox">
     <p>
       <i class="fa fa-danger text-danger"></i>
       <strong>Mapping Conflict:</strong>

src/ui/public/field_editor/field_editor.js

@@ -51,6 +51,7 @@ uiModules
 
       // only init on first create
       self.creating = !self.indexPattern.fields.byName[self.field.name];
+      self.existingFieldNames = self.indexPattern.fields.map(field => field.name); //used for mapping conflict validation
       self.selectedFormatId = _.get(self.indexPattern, ['fieldFormatMap', self.field.name, 'type', 'id']);
       self.defFormatType = initDefaultFormat();