tdf#145875 don't open Insert section dialog when pasting image

tdf#145875 don't open Insert section dialog when pasting image

This happens when we "copy image" in Firefox of the resource which
cannot be accessed without logging in on some website.

In that case we used HTML format and that resulted in pasting
login webpage as a section.

This patch detects simple HTML containing only an image while it also
contains BITMAP format in the clipboard which we can use directly.
That way we paste image data from the clipboard.

Change-Id: Ia2ee7e246f8c71e1d0958c6c955ec056a0a96f8c
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135011
Tested-by: Jenkins
Reviewed-by: Andras Timar <andras.timar@collabora.com>
(cherry picked from commit 0599a73c3c2bffdbfa4e695e2d694f1947215a07)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135013
Reviewed-by: Caolán McNamara <caolanm@redhat.com>