Replace short license text in each file with SPDX license identifier

[ClemensLinnhoff]

Is your feature request related to a problem? Please describe.
Currently, the files have a license short text which is not machine readable, like

/*
 * This Source Code Form is subject to the terms of the Mozilla
 * Public License, v. 2.0. If a copy of the MPL was not distributed
 * with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

Describe the solution you'd like
Replace these short license texts with SPDX identifiers, like

// SPDX-License-Identifier: MPL-2.0

This is a lot shorter and machine readable.

[MatteoRagni]

Hi @ClemensLinnhoff , thanks for the issue.

I'll raise the topic at the next Framework meeting, supporting the request. Seems a good idea.

Thanks

[MatteoRagni]

We discussed the topic, and even if there is a general agreement on the suggestion you proposed, we need to escalate this to ASAM (the copyright owner) to have a final decision. We assigned this to @AsamDiegoSanchez.

[AsamDiegoSanchez]

We have revised it internally and from ASAM perspective we approve it.

[andreaskern74]

Will be implemented in preparation for the official release 1.0.0