Add more trace to understand the project import success rate

[testforstephen]

Add more trace to understand the language server status:

• Measure the import success rate. The indicator we can use is the error diagnostics. If the project root level has error or the Java file has unresolved import errors, we can count it as an import failure.
• Detect the cases of jdk mismatch.

[rgrunber]

Change looks good to me. I noticed some odd behaviour with regard to the jdk mismatch, but it's related to the JVM auto-detection ( #2731 ) that comes from upstream.

I'll file a separate bug to discuss it.

[rgrunber]

😐 forgot to squash. My mistake.