Migrate flimj-ui to Java 21 and openjfx

[elevans]

This PR updates flimj-ui to build on Java 21+ and openjfx, making it functional with Fiji Future (the update to Java 21 for Fiji). Unfortunately, flimj-ui still relies on javascript to create the plots so for now users will need to activate javascript for javafx like so:

$ ./fiji-linux-x64 -Djavafx.allowjs=true

[ctrueden]

@elevans We could add the sys prop setting to the fiji.toml Jaunch config.

[elevans]

Thats right! Now that we ship jaunch it's super easy to config my session. I just added the -Djavafx.allowjs=true flag and I was in business. What was the rest of your message?

[ctrueden]

What was the rest of your message?

I forget! 😅 Might have just been remnants of rephrasing before sending.

Now that we ship jaunch it's super easy to config my session.

I agree, although I also think we'll want to solve apposed/jaunch#38 sooner rather than later, so that update sites can extend the TOML config with their own stuff. Then the update site(s) that ship FLIMJ could include their own TOML extension file with the -Djavafx.allowjs=true.