This change clears out and deletes the _semanticdb folder before compiling. This is similar to how ScalacWorker was already clearing out the _classes directory.
Motivation
I ran into a bug where, when you delete a source *.scala file, it's associated semanticdb file remained and was read-only which caused permission errors when the compiler tried to clear the semanticdb output directory.
Description
This change clears out and deletes the _semanticdb folder before compiling. This is similar to how ScalacWorker was already clearing out the _classes directory.
Motivation
I ran into a bug where, when you delete a source *.scala file, it's associated semanticdb file remained and was read-only which caused permission errors when the compiler tried to clear the semanticdb output directory.