Fixed accessibility issues in Wi-Fi password view in Settings

- Keep the Save button enabled at all times

- Show "*required" or "The password is invalid" to remind the user
  - Show "Password (optional)" to indicate that it can remain unchanged, when modifying Wi-Fi configuration

Bug: 386897596
Bug: 402694144
Flag: EXEMPT bugfix
Test: Manual testing
  atest SettingsUnitTests:AddNetworkFragmentTest
  atest WifiConfigControllerTest \
        WifiConfigController2Test \
        WifiDialogActivityTest
Change-Id: I09b7684674ff376139565fcc196cde8d8d20a864