Java discovery from Windows registry

[ctrueden]

The ImageJ Launcher checks the Windows registry for Java installations. Migrating this code to Jaunch Kotlin would be feasible. Should we do it? Slick would be to support reading from the registry via the same variable syntax. But to do the needed level of indirection might require adding a new TOML section—maybe:

vars = [
	'winregCurrentVersion|HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Development Kit\CurrentVersion',
	'winregJavaHome|HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Development Kit\${winregCurrentVersion}\JavaHome',
]

Kinda hacky for this one feature...