Add SwiftASN1 as dep in CMakeLists file

SwiftPM has added Crypto related functionality to Workspace to
support signing of the swift-syntax prebuilts manifest signing.
This breaks sourcekit-lsp builds on Windows complaining about
SwiftASN1 being missing. Adding a clause here to match the one
in SwiftPM's CMakeLists.txt file.

Author: dschaefer2

CMakeLists.txt

@@ -25,6 +25,7 @@ find_package(ArgumentParser CONFIG REQUIRED)
 find_package(SwiftCollections QUIET)
 find_package(SwiftSyntax CONFIG REQUIRED)
 find_package(SwiftCrypto CONFIG REQUIRED)
+find_package(SwiftASN1 CONFIG REQUIRED)
 
 include(SwiftSupport)