private static int skipWhitespace(String str, int offset, int len) {
        while (offset < len && Character.isSpaceChar(str.charAt(offset))) {
            ++offset;
        }
        return offset;
    }
Creates a new field path entry that digs through all the keys in a map or weighted set, or all the indexes of an array,
an sets the given variable name as it does so (or, if the variable is set, uses the set variable to look up the
collection.

@param variableName The name of the variable to lookup in the collection
@param resultingDataType The value type of the collection we're digging through
@return The new field path entry.
document/src/main/java/com/yahoo/document/FieldPathEntry.java