CMake: Declare ASN1 dependency (#376)

SwiftCrypto depends on SwiftASN1 which is declared in the exports file,
but does not try to find the project, resulting in build failures of
downstream projects that fail to explicitly call
`find_package(SwiftASN1)` before `find_package(SwiftCrypto)`.

Generally, it is recommended that project config files use
`find_dependency` to search for the dependencies of the project they
represent
(https://cmake.org/cmake/help/v3.26/module/CMakeFindDependencyMacro.html).
If the package is already found, either through `find_package` in the
parent project, or through another means, the `find_dependency` call is
a no-op.

Co-authored-by: Cory Benfield <[email protected]>

Author: etcwilde

cmake/modules/SwiftCryptoConfig.cmake.in

@@ -13,5 +13,7 @@
 ##===----------------------------------------------------------------------===##
 
 if(NOT TARGET SwiftCrypto)
+  include(CMakeFindDependencyMacro)
+  find_dependency(SwiftASN1)
   include(@SWIFT_CRYPTO_EXPORTS_FILE@)
 endif()