WildcardQueryNode to expose the positions of the wildcard characters, for easier use in processors and builders [LUCENE-1820]

Change the WildcardQueryNode to expose the positions of the wildcard characters.
This would allow the AllowLeadingWildcardProcessor not to have to knowledge about the wildcard chars \* and ? and avoid double check again.

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Migrated from [LUCENE-1820](https://issues.apache.org/jira/browse/LUCENE-1820) by Luis Alves, updated May 09 2016
Linked issues:
- #2898
- #2641

Start by reading WildcardQueryNode and AllowLeadingWildcardProcessor, then inspect the linked issues #2898 and #2641 for context. The work is done when WildcardQueryNode exposes wildcard-character positions and AllowLeadingWildcardProcessor can use that information instead of independently checking '*' and '?'.

Written by the indexing model from the issue text.