Introduce JBANG_JAVA_VENDOR

[quintesse]

It's preferred to use JBANG_JAVA_VENDOR over JBANG_JDK_VENDOR, so let's add this new JBANG_JAVA_VENDOR env var with the old one as a fallback

[maxandersen]

btw. given devkitman uses distro should we use that instead? because technically multiple vendors can and do have multiple distros...?

so should we make it --java-distro / JBANG_JAVA_DISTRO ?

[quintesse]

Sure, I have no special preference