this fixes the 3 things from the issue - after the screen gets recreated the duplicate name check
and the discard changes dialog both stop working, plus renaming a filtered deck back to its own
name was getting flagged as duplicate.

• Fixes Filtered deck options: name validation and discard-changes dialog stop working after the screen is restored #21463

Purpose / Description

the init block in FilteredDeckOptionsViewModel was returning early whenever there was a previous
state saved:

val previousState = savedStateHandle.get<FilteredDeckOptions>(ARG_DATA)
if (previousState != null) {
    state.update { previousState }
    return@launch
}

problem is two things below that return never ran. decksNames stayed as emptyList() so the
decksNames.contains(name) check inside onDeckNameChange could never be true, and initialState
stayed null so wasStateModified() hit val initial = initialState ?: return false and always
returned false. so after a restore you could type a name that already exist and get no error at
all (Build stays enabled, you just get a raw backend exception when you press it), and pressing
back would throw away all your edits without asking anything.

the third one is unrelated to restore - safeGetDecksNames() uses includeFiltered = true so the
list also has the deck you are editing right now in it. so if you rename an existing filtered deck
and then put the original name back it says "already exists" and disables Rebuild.

Approach

moved decksNames = withCol { safeGetDecksNames() } above the early return since both paths need
it. for initialState i couldnt just read it back from ARG_DATA because that key holds the edited
state, not the original one, so its saved under its own key (ARG_INITIAL_DATA) and read back on
the restore path.

for the third one i used the existing title field - its already documented as the name from when
the deck was first loaded and it doesnt change for the lifetime of the screen, so its exactly what
was needed. only applied it when id != null so it doesnt affect creating new decks.

How Has This Been Tested?

added 3 tests to FilteredDeckOptionsViewModelTest, all of them failed before the fix:

name validation still works after the screen is restored -> expected but was
changed status still works after the screen is restored -> Expected value to be true
reverting to the deck's own name is not a duplicate -> expected but was

for simulating the restore theres a small withRestoredViewModel helper - it builds a view model,
throws it away and builds a second one over the same SavedStateHandle, which is basically what
happens when the VM dies but the handle survives.

also did mutation testing to make sure none of the 3 changes are redundant:

• removed just the initialState restore -> only test 2 failed
• removed the decksNames move + the own name check -> only tests 1 and 3 failed

whole com.ichi2.anki.filtered package is green after (17 tests), ktlint passes.

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner