Should avoid to use SearchEngine in jdt which is not compatible with project settings.

[andxu]

SearchEngine will resolve classes that is not in current project among workspace which makes the source mapping not compatible with project settings.

[akaroml]

This is a fundamental change in how we do source mapping. We'll need to investigate carefully to find an alternative.

[testforstephen]

duplicate with microsoft/vscode-java-debug#121, will discuss the issue there.