Query build system of workspaces to determine best workspace to open a file in

This sets the stage for multi-workspace support. Everything should be handled internally, we are just missing the API to actually open multiple workspaces at this point.

Sources/SKCore/BuildServerBuildSystem.swift

@@ -221,6 +221,26 @@ extension BuildServerBuildSystem: BuildSystem {
   }
 
   public func filesDidChange(_ events: [FileEvent]) {}
+
+  public func fileHandlingCapability(for uri: DocumentURI) -> FileHandlingCapability {
+    guard let fileUrl = uri.fileURL else {
+      return .unhandled
+    }
+
+    // FIXME: We should not make any assumptions about which files the build server can handle.
+    // Instead we should query the build server which files it can handle (#492).
+    let path = AbsolutePath(fileUrl.path)
+    if projectRoot.isAncestorOfOrEqual(to: path) {
+      return .handled
+    }
+
+    let realpath = resolveSymlinks(path)
+    if realpath != path, projectRoot.isAncestorOfOrEqual(to: realpath) {
+      return .handled
+    }
+
+    return .unhandled
+  }
 }
 
 private func loadBuildServerConfig(path: AbsolutePath, fileSystem: FileSystem) throws -> BuildServerConfig {