Support other locations for finding src.zip
Support other locations for finding src.zip

What
===
Support other locations for finding src.zip so that it is found it if
lives at either:
 - JAVA_HOME/lib/src.zip
 - JAVA_HOME/src.zip

Why
===
I've observed in testing that some installations of JVMs include src.zip
in the root, others in a lib/src.zip.

georgewfraser/vscode-javac,georgewfraser/vscode-javac,georgewfraser/vscode-javac