fixup! Tor Browser localization migration scripts.

Bug 42212: Migrate onion service strings to Fluent.

tools/torbrowser/l10n/migrations/bug-42212-onion-services.py

+from fluent.migrate.helpers import transforms_from
+
+
+def migrate(ctx):
+    dtd_path = "torbutton.dtd"
+    properties_path = "torbutton.properties"
+
+    ctx.add_transforms(
+        "tor-browser.ftl",
+        "tor-browser.ftl",
+        transforms_from(
+            """
+onion-site-authentication-prompt-learn-more = { COPY(path, "onionServices.learnMore") }
+onion-site-authentication-prompt-remember-checkbox =
+    .label = { COPY(dtd_path, "torbutton.onionServices.authPrompt.persistCheckboxLabel") }
+onion-site-authentication-prompt-invalid-key = { COPY(path, "onionServices.authPrompt.invalidKey") }
+onion-site-authentication-prompt-setting-key-failed = { COPY(path, "onionServices.authPrompt.failedToSetKey") }
+onion-site-authentication-preferences-learn-more = { COPY(path, "onionServices.learnMore") }
+onion-site-saved-keys-dialog-table-header-key =
+    .label = { COPY(path, "onionServices.authPreferences.onionKey") }
+onion-site-saved-keys-dialog-remove-button = { COPY(path, "onionServices.authPreferences.remove") }
+onion-site-saved-keys-dialog-remove-keys-error-message = { COPY(path, "onionServices.authPreferences.failedToRemoveKey") }
+""",
+            dtd_path=dtd_path,
+            path=properties_path,
+        ),
+    )