The idea here is to unify the different ways in which we can currently set options on SourceKit-LSP in a scalable way: Environment variables, command line arguments to `sourcekit-lsp` and initialization options.
The idea is that a user can define a `~/.sourcekit-lsp/.sourcekit-lsp` file (we store logs in `~/.sourcekit-lsp/logs` on non-Darwin platforms), which will be used as the default configuration for all SourceKit-LSP instances. They can also place a `.sourcekit-lsp` file in the root of a workspace to configure SourceKit-LSP for that project specifically, eg. setting arguments that need to be passed to `swift build` for that project and which thus also need to be set on SourceKit-LSP.
For compatibility reasons, I’m mapping the existing command line options into the new options structure for now. I hope to delete the command line arguments in the future and solely rely on `.sourcekit-lsp` configuration files.
Environment variable will be migrated to `.sourcekit-lsp` in a follow-up commit.
The new approach has a few advantages over the olde TIBS-based approach:
1. The source file being tested is defined within the test case itself and not in a separate file, which makes it easier to understand the test case since the auxiliaury file doesn’t need to be opened. Finding it inside `Sources/SKTestSupport/INPUTS` is already hard for people that are not familiar with the codebase.
2. The build setup is significantly simpler since it doesn’t rely on `ninja`. It is thus easier to understand what is run during the test.
3. We can use the emoji location markers to refer to test locations, like we do for files that are opened using `TestSourceKitLSPClient.openDocument`.
This commit only migrates call hierarchy testing to the new design. If we like it, I’ll migrate the other test workspaces as well.
Request types should always have the suffix Request and notifications
should end with Notification.
Also moved all request and notification types into separate folders to
reduce the number of files in the LanguageServerProtocol folder.
