Better plain text copy

[vmiklos]

Describe the Bug

Currently we give HTML to the browser when it comes to copy&paste, and then the browser converts that HTML to plain text. This is worse than our own plain text export, so we should use that instead.

Steps to Reproduce

1. Create a new Writer document with a normal paragraph and 3 bullets.
2. Select all.
3. Copy
4. Paste somewhere that wants a plain text format.

Expected Behavior

Something similar to Collabora Office:

Bullets:
    • a
    • b
    • c

Actual Behavior

HTML -> plain text conversion is done by browser, e.g. Firefox produces:

Bullets:

	a
	b
	c

Additional Context

A related problem is that when we determine if the current selection is simple or complex, then Writer marks inline images as complex (good), but anchored images are still simple (bad). That should be fixed first, given it allows easier testing that way.

This is a general problem, affecting both Firefox and Chrome.

[vmiklos]

https://gerrit.libreoffice.org/c/core/+/164453 for the related problem around a simple selection that has an image.

[vmiklos]

#8569 fixes the complex case, this should be OK now.