fix(deck-options): add progress bar to stop flickering

[david-allison]

Purpose / Description

This is the last of a series of 3 pull requests:

• refactors which can go in before the backend bump
• bump the backend and fix Deck Options
• (we are here) use the new backend functionality to fix Deck Options loading

Fixes

• Fixes Deck Options: White screen flicker in night mode #14194 - deck options no longer flicker

Approach

deckOptionsReady allows us to know exactly when the backend is ready, instead of showing the WebView in PageWebViewClient.onPageFinished.

Stop showing the WebView in onPageFinished, and wait for deckOptionsReady

A CircularProgressIndicator has been added as the wait is noticeable (~300ms)

Once the WebView is shown, hide the Progress Bar

promiseToWaitFor and :page-fully-loaded are also removed as unused, and these were primarily for DeckOptions

How Has This Been Tested?

Personal S21 (Android 14)

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

[mikehardy]

seems good - only query is about handling e-ink, I think for them just no indicator and 300ms is...I dunno ...good performance for an e-ink device? so it's fine to just let it sit for a moment before webview is visible?

[mikehardy]

Ah, cool re: respecting system settings. I guess this is a benefit of "not fighting the platform", or stated positively: "using platform built-in features", they already do so much of what you want. LGTM then

[david-allison]

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