CMake code completion: Add missing chars to be escaped

Summary:
List of chars to be escaped is taken from: https://cmake.org/Wiki/CMake/Language_Syntax

> To use literally any of "()#$^, escape the character with a backslash

Test Plan: created a file foo"()#$^.cpp, the chars are escaped properly.

Reviewers: #kdevelop, kfunk

Reviewed By: #kdevelop, kfunk

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D6689

CCBUG: 338196