Test Maven build in CI

[lhstrh]

This PR adds testing of the Maven build to our CI workflow. An initial run of the new workflow that the build had already broken. Fixes are included. Specifically:

Problem 1:

Error:  /home/runner/work/lingua-franca/lingua-franca/org.lflang/src/org/lflang/generator/rust/RustTypes.kt:[58,37] Super calls to Java default methods are prohibited in JVM target 1.6. Recompile with '-jvm-target 1.8'

Solution 1: bump Kotlin from 1.4.10 to 1.6.10

Problem 2:

Error:  /home/runner/work/lingua-franca/lingua-franca/org.lflang.diagram/src/org/lflang/diagram/lsp/Progress.java:[104] 
Error:  	client.notifyProgress(new ProgressParams(Either.forRight(token), Either.forLeft(notification)));
Error:  	                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error:  The constructor ProgressParams(Either.forRight(token), Either.forLeft(notification)) is undefined
Error:  1 problem (1 error)

Solution 2: revert ee19274 (already done in master)

Fixes #861

[cmnrd]

This addresses the Maven part of #575, right? I wonder if we should close this issues, as there seems to be no solution for testing the eclipse build.