Extract TextMessageView into a separate file (#759)

* Extract `TextMessageView` into a separate file

* Remove dead code

bitchat/_PreviewHelpers/BitchatMessage+Preview.swift

@@ -0,0 +1,27 @@
+//
+// BitchatMessage+Preview.swift
+// bitchat
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Foundation
+
+extension BitchatMessage {
+    static var preview: BitchatMessage {
+        BitchatMessage(
+            id: UUID().uuidString,
+            sender: "John Doe",
+            content: "Hello",
+            timestamp: Date(),
+            isRelay: false,
+            originalSender: nil,
+            isPrivate: false,
+            recipientNickname: "Jane Doe",
+            senderPeerID: nil,
+            mentions: nil,
+            deliveryStatus: .sent
+        )
+    }
+}

bitchat/_PreviewHelpers/PreviewKeychainManager.swift

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+//
+// PreviewKeychainManager.swift
+// bitchat
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Foundation
+
+final class PreviewKeychainManager: KeychainManagerProtocol {
+    private var storage: [String: Data] = [:]
+    init() {}
+    
+    func saveIdentityKey(_ keyData: Data, forKey key: String) -> Bool {
+        storage[key] = keyData
+        return true
+    }
+    
+    func getIdentityKey(forKey key: String) -> Data? {
+        storage[key]
+    }
+    
+    func deleteIdentityKey(forKey key: String) -> Bool {
+        storage.removeValue(forKey: key)
+        return true
+    }
+    
+    func deleteAllKeychainData() -> Bool {
+        storage.removeAll()
+        return true
+    }
+    
+    func secureClear(_ data: inout Data) {}
+    
+    func secureClear(_ string: inout String) {}
+    
+    func verifyIdentityKeyExists() -> Bool {
+        storage["identity_noiseStaticKey"] != nil
+    }
+}