The timers were racy and on Windows we would get the updated build targets / build settings before we expect them. Change the tests to explicitly tell the build server when to change the targets / settings it reports by sending it a `workspace/didChangeWatchedFiles` notification.
This should also speed up the tests because we don’t have a 1s timer anymore.
The build server is automatically shut down using a background task when `BuildSystemManager` is deallocated.
This, however, leads to possible race conditions where the shutdown task might not finish before the test is done, which could result in the connection being reported as a leak. To avoid this problem, we want to explicitly shut, down the build server when the `SourceKitLSPServer` gets shut down.
The interaction to an out-of-process BSP server still went through the `BuildServerBuildSystem`, which doesn’t forward all messages to the build system and uses the old push-based model for build settings.
If we discover that the BSP server supports the new pull-based build settings model, we now forward all methods to it directly, without going through `BuiltInBuildSystemAdapter`, which has been renamed to `LegacyBuildServerBuildSystem`.
rdar://136106323
rdar://127606323
rdar://126493405
Fixes#1226Fixes#1173
