Text redaction annotation support

[pcorless]

Text redaction annotation support would allow a user to select the respective annotation tool, highlight some text as one would do with the regular highlight annotation tool. But in this case the selection colour would be black and it would be opaque. A user could work their way though the document redacting as needed. The user would then likely need to take advantage of an export redacted document. The dialog would need a few options like encryption or signing options and the ultimately a save/burn button. The save would take advantage of the GH-233 and over write any existing objects with new content.

The redaction text annotation type would take care of the content stream marking and removal of content. There are a couple ways this can be done. The simplest way would probably be to remove the text, and the pre and post text locations updated. A highlight annotation would be drawn as an overlay that would give the black marker effect based on the removed text bounds.

Rewriting the content stream might be as simple as checking if each StringObject intersects the annotation bounds. Individual rules could then be written on how to split the content stream and carry the horizontal displacement to avoid any changes to page layout.

Dependent on GH-233

[gtache]

After a first test, everything seems to work well, thanks a lot!
Our only proposition for now would be to directly propose to the user to export the document instead of saving it in the popup, instead of telling them to go to file->export manually.
I guess the user could choose between yes/no/cancel in this case (yes -> export, no -> save, cancel -> do nothing)

[pcorless]

Good to hear and good point. I'll make the change the dialog.

[pcorless]

Merged changes into the GH-314. Fill add future refinements and bug fixes to this new ticket which has both text and image redaction support merged.