OSLog is the suggesting logging solution on Apple platforms and we should be using it there, taking advantage of the different log levels and privacy masking.
Switch sourcekit-lsp to use OSLog on Apple platforms and implement a logger that is API-compatible with OSLog for all uses in sourcekit-lsp and which can be used on non-Darwin platforms.
The goal of this commit is to introduce the new logging API. There are still improvements about what we log and we can display more privacy-insensitive information after masking. Those changes will be in follow-up commits.