Tweak java code generated for the analysis server protocol to avoid org.apache.commons.lang3.StringUtils

[jacob314]

org.apache.commons.lang3.StringUtils is prohibited by the flutter intellij plugin for likely plausible reasons. A good replacement is com.google.common.base.Joiner

Using generated code that imports org.apache.commons.lang3.StringUtils results in the following output.

Fyi @scheglov

Check for bad imports
Checking for import of "com.android.annotations.NonNull"...
  none found
Checking for import of "io.netty."...
  none found
Checking for import of "javax.annotation.Nullable"...
  none found
Checking for import of "org.apache.commons.lang3.StringUtils"...
Found proscribed imports:
src/org/dartlang/analysis/server/protocol/ExtractWidgetFeedback.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/ExtractWidgetOptions.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/FlutterOutline.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/FlutterOutlineAttribute.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/FlutterWidgetProperty.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/FlutterWidgetPropertyEditor.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/FlutterWidgetPropertyValue.java:import org.apache.commons.lang3.StringUtils;
src/org/dartlang/analysis/server/protocol/FlutterWidgetPropertyValueEnumItem.java:import org.apache.commons.lang3.StringUtils;