Use Reflections library rather than Jar class scanning

[TheLimeGlass]

Uses Reflections library rather than Jar class scanning.

Not all projects that implement the skript-parser will use Jars.
Using Reflections library also allows developers to define custom url types before skript-parser scans, such as NeoForge using Union URL Type. I need to register Union URL Type to Reflections before skript-parser.

For example Scroll https://github.com/ScrollLang on NeoForge and Fabric have development options to load the build/ classes for injection hotswapping. This allows avoiding the need to restart the Minecraft client for non new method changes.

So skript-parser will throw an exception as there is no source Jar (it's excluded as a library jar in NeoForge);

java.lang.IllegalArgumentException: URI scheme is not "file"
	at java.base/java.io.File.<init>(File.java:423) ~[?:?]
	at MC-BOOTSTRAP/skript.parser.alpha5/io.github.syst3ms.skriptparser.util.FileUtils.getJarFile(FileUtils.java:214) ~[skript-parser-alpha5.jar%23220!/:alpha5]
	at MC-BOOTSTRAP/skript.parser.alpha5/io.github.syst3ms.skriptparser.Parser.init(Parser.java:102) ~[skript-parser-alpha5.jar%23220!/:alpha5]

• Also adds the ability to define the main root folder for /addon/ scanning in the init method.
• Needs to use gradleup's shadow plugin to shadow in Reflections library.
• Bumps Java version from 11 to 17
• Will bump the gradle version and Java to 21 in another pull request. Current gradle 8.3 can operate up to Java 20.
• Forced to update the GitHub versions (v4) for actions cache and setup-java as the current ones are removed (v2).