Improved logging setup

[award999]

Right now the Swift extension is writing log messages to the Swift output channel and holding EVERY log message in memory to eventually write to a file if they run the capture diagnostics command. Following the same approach as proposed at llvm/llvm-project#146880, we will use winston to always log messages of all levels to a file so the log can still be acquired for past runs, and then we will not need to hold all messages in memory. Will also clean up our interfaces so we don't have varying functions like "appendLine", "log", "logDiagnostic", etc. to pick from.