Add automatic module name

[TheDGOfficial]

Description

Adds an automatic module name, that is, used as module name when Skript is on the modulepath on Java 9+.

If the jar is not modular (does not contain module-info.class) and does not have a Automatic-Module-Name entry on META-INF/MANIFEST.MF, then the module name is determined by file name.

Publishing non modular artifacts (not containing module-info.class) that also doesn't contain Automatic-Module-Name to any repository and using them as libraries on projects is discouraged, and will most likely cause a warning to be thrown.

The filename based module name is normally Skript on releases published in GitHub Releases, but people can alter them and name it whatever they want.

Adding an Automatic-Module-Name will break the current modular projects that requiring Skript via its module name derived from file name (i.e. requires Skript; in module-info.java), because in this PR I used ch.njol.skript as module name, so the correct code should be requires ch.njol.skript; after this PR. We can do Automatic-Module-Name: Skript to not break anything and just make it not dependant on file name, but for naming conventions it should be ch.njol.skript.

Note that, this will not change anything on < Java 9 or even Java 9+, on non modular projects.

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Target Minecraft Versions: any
Requirements: none
Related Issues: none