CI: Backport GitHub Actions setup from master

Removes AppVeyor and all Travis jobs but the iOS one, which hasn't been ported
to GitHub Actions yet (should be done soon).

Backports new style scripts from `master` branch too to do the same checks.

misc/scripts/copyright_headers.py

@@ -0,0 +1,95 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+import sys
+
+header = """\
+/*************************************************************************/
+/*  $filename                                                            */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+"""
+
+fname = sys.argv[1]
+
+# Handle replacing $filename with actual filename and keep alignment
+fsingle = fname.strip()
+if fsingle.find("/") != -1:
+    fsingle = fsingle[fsingle.rfind("/") + 1 :]
+rep_fl = "$filename"
+rep_fi = fsingle
+len_fl = len(rep_fl)
+len_fi = len(rep_fi)
+# Pad with spaces to keep alignment
+if len_fi < len_fl:
+    for x in range(len_fl - len_fi):
+        rep_fi += " "
+elif len_fl < len_fi:
+    for x in range(len_fi - len_fl):
+        rep_fl += " "
+if header.find(rep_fl) != -1:
+    text = header.replace(rep_fl, rep_fi)
+else:
+    text = header.replace("$filename", fsingle)
+text += "\n"
+
+# We now have the proper header, so we want to ignore the one in the original file
+# and potentially empty lines and badly formatted lines, while keeping comments that
+# come after the header, and then keep everything non-header unchanged.
+# To do so, we skip empty lines that may be at the top in a first pass.
+# In a second pass, we skip all consecutive comment lines starting with "/*",
+# then we can append the rest (step 2).
+
+fileread = open(fname.strip(), "r")
+line = fileread.readline()
+header_done = False
+
+while line.strip() == "":  # Skip empty lines at the top
+    line = fileread.readline()
+
+if line.find("/**********") == -1:  # Godot header starts this way
+    # Maybe starting with a non-Godot comment, abort header magic
+    header_done = True
+
+while not header_done:  # Handle header now
+    if line.find("/*") != 0:  # No more starting with a comment
+        header_done = True
+        if line.strip() != "":
+            text += line
+    line = fileread.readline()
+
+while line != "":  # Dump everything until EOF
+    text += line
+    line = fileread.readline()
+
+fileread.close()
+
+# Write
+filewrite = open(fname.strip(), "w")
+filewrite.write(text)
+filewrite.close()