Add support for a multi-release jar

[mbbergma]

When upgrading from java8 to Java11+ one has to treat the mssql-jdbc dependency different to other jar dependencies, since as part of the java upgrade you will have to also upgrade the application itself to use the newer jar dependency.

Java supports multi-release jars https://openjdk.org/jeps/238, i.e. jars that contain classes for both java8 and java11+, why can this project not be shipped with a single jar that is backwards compatible with older java versions?

[tkyc]

why can this project not be shipped with a single jar that is backwards compatible with older java versions?

That's not something we've explored yet, but does sound useful to do. I'll bring this up to the team at the next triage. Marking this as a potential enhancement for now.