Start converting libraries to use FoundationEssentials (apple#676)

This helps on binary size if we can successfully get all Foundation
imports out of our dep chain. It seems Foundation brings in a 30MiB ICU
blob, which bloats vmexec and vminitd.

Author: dcantah

Sources/ContainerizationOS/AsyncSignalHandler.swift

@@ -14,9 +14,17 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
-import Foundation
+import Dispatch
 import Synchronization
 
+#if canImport(Musl)
+import Musl
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(Darwin)
+import Darwin
+#endif
+
 /// Async friendly wrapper around `DispatchSourceSignal`. Provides an `AsyncStream`
 /// interface to get notified of received signals.
 public final class AsyncSignalHandler: Sendable {

Sources/ContainerizationOS/File.swift

@@ -14,7 +14,19 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
-import Foundation
+#if canImport(Musl)
+import Musl
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(Darwin)
+import Darwin
+#endif
+
+#if canImport(FoundationEssentials)
+import struct FoundationEssentials.URL
+#else
+import struct Foundation.URL
+#endif
 
 /// Trivial type to discover information about a given file (uid, gid, mode...).
 public struct File: Sendable {
@@ -52,7 +64,7 @@ public struct File: Sendable {
 /// `FileInfo` holds and provides easy access to stat(2) data
 /// for a file.
 public struct FileInfo: Sendable {
-    private let _stat_t: Foundation.stat
+    private let _stat_t: stat
     private let _path: String
 
     init(_ path: String, stat: stat) {

Sources/ContainerizationOS/Keychain/KeychainQuery.swift

@@ -15,7 +15,11 @@
 //===----------------------------------------------------------------------===//
 
 #if os(macOS)
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 /// Holds the result of a query to the keychain.
 public struct KeychainQueryResult {

Sources/ContainerizationOS/Keychain/RegistryInfo.swift

@@ -14,7 +14,11 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 /// Holds the stored attributes for a registry.
 public struct RegistryInfo: Sendable {

Sources/ContainerizationOS/Linux/Binfmt.swift

@@ -14,7 +14,11 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 #if canImport(Musl)
 import Musl

Sources/ContainerizationOS/Linux/Capabilities.swift

@@ -15,7 +15,12 @@
 //===----------------------------------------------------------------------===//
 
 import CShim
+
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 // MARK: - Configuration Types
 

Sources/ContainerizationOS/Linux/Epoll.swift

@@ -15,7 +15,11 @@
 //===----------------------------------------------------------------------===//
 
 #if os(Linux)
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 #if canImport(Musl)
 import Musl

Sources/ContainerizationOS/Mount/Mount.swift

@@ -15,7 +15,12 @@
 //===----------------------------------------------------------------------===//
 
 import CShim
+
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 #if canImport(Musl)
 import Musl

Sources/ContainerizationOS/POSIXError+Helpers.swift

@@ -14,7 +14,19 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+#if canImport(Musl)
+import Musl
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(Darwin)
+import Darwin
+#endif
+
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 extension POSIXError {
     public static func fromErrno() -> POSIXError {

Sources/ContainerizationOS/Path.swift

@@ -14,7 +14,11 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 /// `Path` provides utilities to look for binaries in the current PATH,
 /// or to return the current PATH.