Update Copyright statements in Code Files

As discussed in the comments on PR #6593, it may be time to update the copyright statements in the code files.
I am willing to do this, if somebody could guide me a bit about what I should do exactly.

Should I just update them all to the following:

//=============================================================================
//  MuseScore
//  Music Composition & Notation
//
//  Copyright (C) 2020 MuseScore BVBA and others
//
//  This program is free software; you can redistribute it and/or modify
//  it under the terms of the GNU General Public License version 2.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program; if not, write to the Free Software
//  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
//=============================================================================

Of course in the cmake files # instead of //.
I won't touch the "third-party" files.

Some files have quite a different version:

//  This program is free software; you can redistribute it and/or modify
//  it under the terms of the GNU General Public License version 2
//  as published by the Free Software Foundation and appearing in
//  the file LICENCE.GPL

Should I update those too?

Some files say for example Copyright (C) 2002-2018. Should we lose the 2002- ?

And some files say

//  MusE Score
//  Linux Music Score Editor

Is it okay to get rid of these "traces of history"?

Whenever I come across a case which isn't straight-forward, I will post a comment in this issue.

The advantage of having uniformity in all files, is that we can update them in the future by just using "find and replace".