Test bugfixes: preparation for GH action migration

[sdedic]

A follow-up to #4921.

The most important fix is a fix to nbjavac task that prevents classes like $JsCallback$ and similar to be deleted just before an incremental compilation because they are considered inner classes (without a matching outer class).

I've added additional logging to both server and client, because some thrown errors are wrapped into uninformative "Internal error". Added possibility to log-trace LSP messages (enabled by System property)

I've cleaned up the test a little:

• the exception about missing Groovy support turned into a WARNING line, if the client demands Groovy enabled, but it is simply not available. Other Reflective exceptions show stacktrace.
• fixed error that manifested by a print about 'not normalized' license template filename/path
• suppressed SocketClosed exceptions in test output
• fixed potential CNFE when running on JDK11: Truffle could not access sun.misc.Unsafe during script engine initialization

[mbien]

looks good to me. Appreciate the fixes to the exception logging too - this makes it easier to find issues in the log when something happens.

[mbien]

excellent! This means we have another job which could run on JDK 11+ (e.g in a matrix).

[sdedic]

Not really - there are still some failing tests, I asked @dbalek for an assistance as the failure seems to be deeply burried in javac binding infrastructure. But it's definitely a step forward.

[mbien]

lets merge this this week so that we can finish up the migration PR and open it for review. Travis will end free support for open source projects, apache projects have to migrate before the end of this year.