Fix insane delay in report items creation

Summary:
Fix insane delay in report items creation by not instantiating hi-resolution QPrinter object for each item.

To be honest I am not understanding the whole word-wrapping algorithm used here.

Test Plan:
Approach 1: Run KEXI and create report with large number of pages. Use at
least one text element.
Before the fix there's noticeable O(N) delay.

Approach 2: Also if we enter static value for the text item the kreportexample
app, there is noticeable delay on each key press before this fix.

Expected: all is smooth after the fix.

Reviewers: piggz

Reviewed By: piggz

Subscribers: Kexi-Devel-list

Tags: KReport

Differential Revision: https://phabricator.kde.org/D25108