fdo#78502: writerfilter: RTF import: handle \u keyword inside levelnumbers

The ";" terminates an entry and shall not be inserted as text,
even if some over-engineered producer encodes it as {\uc1 \u59 ?}.

Also, remove the special-casing of the \leveltext destination, since the
bugdoc does contain \uc inside it and it's not obvious why that should
be ignored.

(cherry picked from commit e93f0852477b44df986807860c821319a921b199)

fdo#78502: actually empty parameter to getParagraph() is not tested
(cherry picked from commit b9dca968c6fd0ab5ca140c65b0e54d153cd34986)

Change-Id: I1e19c9df39597cb1b22bbda97853c829d7812e29
Reviewed-on: https://gerrit.libreoffice.org/10396
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>