KDevelop : support whitespace between the '#' and 'include' (or 'import')

Summary:
The C/C++ parser fails to recognise include statements where the hash symbol has whitespace between it and the include/import command.

This patch fixes that.

BUG: 394200
FIXED-IN: 5.2.2

Test Plan: Works as expected.

Reviewers: #kdevelop, antonanikin, kfunk

Reviewed By: #kdevelop, antonanikin, kfunk

Subscribers: kfunk, kdevelop-devel

Tags: #kdevelop

Differential Revision: https://phabricator.kde.org/D12903