When close Eclipse project, don't remove element information

When close project, these files are shown as "removed" from Eclipse, which prompts a reindex.

Since the project is closed, we lose the "element" information (such as the method name). However, there's no reason to remove this. It will be stale if the project is modified outside of Eclipse, but that's okay.

This will allow closing and opening projects without requiring a reindex of these files. Also, we won't lose the valuable "element" information.

If the file is modified outside of Eclipse, we'll reindex that file, which will remove the element info, but this is acceptable, since the info cannot be determined until the project is openned again.

Once the project is opened, this information should be reindexed.

Start by tracing how Eclipse project close and reopen events handle indexed files and element information. Verify that closing a project does not mark its files removed or trigger reindexing, while reopening restores current information and external modifications cause the affected files to be reindexed.

Written by the indexing model from the issue text.