Apply copyright notices to new files

.../kotlin/androidx/compose/material/OutlinedTextFieldExt.kt

...briarproject/briar/desktop/conversation/AttachmentItem.kt

...otlin/org/briarproject/briar/desktop/login/ErrorScreen.kt

...org/briarproject/briar/desktop/login/ErrorSubViewModel.kt

...tlin/org/briarproject/briar/desktop/login/FormScaffold.kt

...otlin/org/briarproject/briar/desktop/login/LoadingView.kt

...org/briarproject/briar/desktop/login/LoginSubViewModel.kt

...arproject/briar/desktop/login/RegistrationSubViewModel.kt

...lin/org/briarproject/briar/desktop/login/StartupScreen.kt

.../org/briarproject/briar/desktop/login/StartupViewModel.kt

...lin/org/briarproject/briar/desktop/login/StrengthMeter.kt

...otlin/org/briarproject/briar/desktop/utils/ImagePicker.kt

.../org/briarproject/briar/desktop/TestStartupWithAccount.kt

...oject/briar/desktop/TestStartupWithUnwritableDirectory.kt

...g/briarproject/briar/desktop/TestStartupWithoutAccount.kt