Export Commands Overhaul

[rtfmkiesel]

This is the update to #463, which was made to address #311.

I've implemented @yhatt's feedback (#311 (comment)) into this branch.

There are now 3 export commands:

• markdown.marp.exportAs which will open a save dialog (as it is now)
• markdown.marp.exportQuick which will quick export into the document directory with the file type being determined by the setting exportType
• markdown.marp.exportToSelectedFormat which will quick export into the document directory with the user being asked first for which file type should be used

The old markdown.marp.export is mapped to markdown.marp.exportAs for legacy/compatibility reasons.

I did not touch the existing functions doExport and saveDialog.startExport only exists to have a target for unit tests when calling exportQuick or exportToSelectedFormat.

I also had to run npm audit fix to update two dependencies.

Please note, I've not worked with jest before so the unit test may need improvement.

[rtfmkiesel]

I find the naming of the commands to confusing. My proposal would be the following:

• Export Slide Deck to ... (file dialog)
• Export Slide Deck as ... (Quick) (format selection + quick export)
• Export Slide Deck (Quick) (quick export based on settings)