Reindexing for async indexes should only be done when IndexUpdate is running in async mode

Currently any commit involving IndexUpdate consider an index for reindexing if

• Reindex flag is true
• OR before state is not there

This worked fine before hybrid indexes as pure async indexes were not considered for update for sync commits. However with hybrid indexes such async indexes also participate in sync commit. However in such cases they are only meant to perform incremental indexing and not handle the reindex case. So IndexUpdate should only consider an index for reindexing if

• IndexUpdate is in async mode i.e. async != null and index has async flag set