Improve Text Layer Handling

[qgib]

Author Name: Brett Carlock (@Saijin-Naib)
Original Redmine Issue: 21798

Redmine category:data_provider/delimited_text_

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It'd be great to have the ability to change/enable/disable the various behaviors/features of Text Layers after they've been imported to a project.

For instance, being able to toggle on/off Watch File, Subset Indexing, changing Geom columns (if a file gets modified down the line), Column Type Detection, etc.

Currently, to enable watching a file I'd have to remove/re-add it, breaking all the joins in my current project. Instead, in order to reflect updates, I now close/re-open my QGIS project.