[License] Inaccurate mentions of secondary license name and SPDX

[marcdumais-work]

Bug Description:

@SpessartZiegler recently reported a couple problems with our licenses:

• We have had the SPDX wrong for our secondary license [1]. Also in places, we have that license name wrong. I checked for the primary license (EPL) and found no similar issues with our naming/referencing it. update: Wayne confirmed that the current SPDX is not perfect but better than the deprecated version.
• When we recently split the license file into two, the text of the secondary license got accidently changed, e.g. now it contains an extra, Oracle-specific pargraph. We should re-align on the official license text.

In addition, I think that the naming of the LICENSE-GPL file is likely to cause confusion and that a name that's more in-line with the fact that the secondary license is specifically the "classpath exception" variant, would be an improvement.

Some more details:

In the package.json files and in the header of source files, we have the SPDX[1], and a slightly better one suggested by Wayne :

• current: SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
• better: SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-only WITH Classpath-exception-2.0

Links:

• [1]: https://spdx.org/licenses/GPL-2.0-with-classpath-exception.html
• [2]: https://spdx.org/licenses/EPL-2.0.html

Steps to Reproduce:

Additional Information

• Operating System:
• Theia Version: