Integrate launch4j into maven build process

[ralfgerlich]

Currently, there are two open issues (#991 and #670), which seem to be related to non-up-to-date launch4j artefacts (Digital.exe, Digital_nod3d.exe). It seems that in the current build process these two artefacts are generated manually and imported into the distribution subdirectory.

There is a maven plugin (https://github.com/orphan-oss/launch4j-maven-plugin) that allows running launch4j from maven, and thus possibly also in the CI/CD pipeline.

This PR introduces launch4j into the Maven build, building both exes in the target directory and pulling them in appropriately for assembly. It also fixes a few warnings from the assembly plugin regarding superfluous slashes in <outputDirectory> settings.

So far, I have tested it successfully on a Windows 11 Professional install (Version 22H2, build 22621.2283) with openjdk 17.0.8.1 (Microsoft Build). The generated launchers find my installed JRE and run Digital. mvn verify also runs through, which to me would imply that Digital would be usable with this JRE version.

Some of the configuration for launch4j had to be adapted, as there have been changes leading up to Version 3.50:

• <path> needs to be explicitly set, with the default suggested by launch4j being %JAVA_HOME%;%PATH%.
• <bundledJre64Bit> and <runtimeBits> have been removed and replaced by <requires64Bit>, which is false by default, but was kept for documentation purposes.
• <bundledJreAsFallback> had been removed, it had been set to false anyway as no JRE is included. If a JRE were to be included, changing the <path> setting appropriately would introduce the fallback.
• <jdkPreference> has been replaced by <requiresJdk>, which is false by default.

[ralfgerlich]

Just checked with Adoptium Eclipse Temurin 17.0.8.1+1 (after uninstalling the Microsoft openjdk), and the exes also work (even for opening .dig files by associating them with Digital.exe).