ipn: generate LoginProfileView and use it instead of *LoginProfile where appropriate

Conventionally, we use views (e.g., ipn.PrefsView, tailcfg.NodeView, etc.) when
dealing with structs that shouldn't be mutated. However, ipn.LoginProfile has been
an exception so far, with a mix of passing and returning LoginProfile by reference
(allowing accidental mutations) and by value (which is wasteful, given its
current size of 192 bytes).

In this PR, we generate an ipn.LoginProfileView and use it instead of passing/returning
LoginProfiles by mutable reference or copying them when passing/returning by value.
Now, LoginProfiles can only be mutated by (*profileManager).setProfilePrefs.

Updates #14823

Signed-off-by: Nick Khyl <nickk@tailscale.com>

ipn/ipn_clone.go

@@ -17,6 +17,29 @@ import (
 	"tailscale.com/types/ptr"
 )
 
+// Clone makes a deep copy of LoginProfile.
+// The result aliases no memory with the original.
+func (src *LoginProfile) Clone() *LoginProfile {
+	if src == nil {
+		return nil
+	}
+	dst := new(LoginProfile)
+	*dst = *src
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _LoginProfileCloneNeedsRegeneration = LoginProfile(struct {
+	ID             ProfileID
+	Name           string
+	NetworkProfile NetworkProfile
+	Key            StateKey
+	UserProfile    tailcfg.UserProfile
+	NodeID         tailcfg.StableNodeID
+	LocalUserID    WindowsUserID
+	ControlURL     string
+}{})
+
 // Clone makes a deep copy of Prefs.
 // The result aliases no memory with the original.
 func (src *Prefs) Clone() *Prefs {