File formats for 1.0

Hi everyone,

we're looking for people to try and open their legacy Corel, Illustrator
and other files with Inkscape 1.0 (or to look things up in the code and
tell us if they *should* be working).

Previously, these formats were (also) handled via extensions, and
uniconvertor was required for it to work.

Specifically, we're asking about opening:

* Adobe Illustrator 8.0 and below (UC) (*.ai) (I think those could be
renamed to pdf and would then open, but I have no example files to try
it out)

* Corel DRAW Compressed Exchange files (UC) (*.ccx)

* Corel DRAW 7-X4 files (UC) (*.cdr) [cdr imports, but this specific
version?]

* Corel DRAW 7-13 template files (UC) (*.cdt)

* Computer Graphics Metafile files (UC) (*.cgm)

* Corel DRAW Presentation Exchange files (UC) (*.cmx)

* HP Graphics Language Plot file [AutoCAD] (UC) (*.plt)

* Dia Diagram (*.dia)

Please reply at https://gitlab.com/inkscape/inbox/issues/1213 if you can
help with any of these.

(we need the info for the file bindings and for the release notes)

Hope someone can help,
 Maren