Fix protocol for EXTRACT_LOCAL_VARIABLE and coveringExpressionOffsets/lengths.

pkg/analysis_server/tool/spec/spec_input.html

Index: pkg/analysis_server/tool/spec/spec_input.html
diff --git a/pkg/analysis_server/tool/spec/spec_input.html b/pkg/analysis_server/tool/spec/spec_input.html
index 8c349e32670dc9f911a74d3afba7f4b7fc72191c..7c8f75333ad26d9c2642ad2f2c8a60e257816db1 100644
--- a/pkg/analysis_server/tool/spec/spec_input.html
+++ b/pkg/analysis_server/tool/spec/spec_input.html
@@ -4035,14 +4035,14 @@
           complete expression.
         </p>
         <feedback>
-          <field name="coveringExpressionOffsets">
+          <field name="coveringExpressionOffsets" optional="true">
             <list><ref>int</ref></list>
             <p>
               The offsets of the expressions that cover the specified
               selection, from the down most to the up most.
             </p>
           </field>
-          <field name="coveringExpressionLengths">
+          <field name="coveringExpressionLengths" optional="true">
             <list><ref>int</ref></list>
             <p>
               The lengths of the expressions that cover the specified