Expandable ongoing notification: Now / Average breakdown on pull-down (#194)

[almothafar]

Follow-up to #192 (which made the title the stable headline and the content the volatile details). This turns the ongoing status notification into a BigTextStyle two-state notification — the mockup-approved v2 shape.

Collapsed (the glance)

• Title (unchanged): 85% · Discharging / 85% · Charging.
• Content: rate/power · current · time —
  • discharging: 9%/h · −250 mA · ~9h 27m remaining
  • charging: ~18 W · +2000 mA · ~1h 0m to full
  • Adds the instantaneous current; temperature moves to the expanded view; "left" → "remaining" (matches the details table).

Expanded (pull down)

Labelled label: value lines:

Discharging — Now: −250 mA / Average: −338 mA · 9%/h / Time remaining: ~9h 27m / Temperature: 34.6 °C
Charging — Now: +2000 mA · ~10 W / Average: +1900 mA / Time to full: ~1h 0m / Temperature: 34.6 °C

• Now = instantaneous current (+ wattage while charging); Average = the windowed-average current (from Current row flickers and disagrees between surfaces — show moment value with windowed average, gate visibility on the average #173).
• Honest adjustment from the mock: the app computes a single smoothed rate (which is itself an average), so there's no separate instantaneous %/h — the %/h rides the Average line rather than being faked onto Now. When the average current isn't ready yet, the %/h gets its own Drain rate: line so it isn't lost.
• Every line is dropped when its data is absent; the notification is only made expandable when the breakdown is genuinely multi-line (so Temperature-only never shows a pointless expand chevron).

Arabic / RTL

The Latin values (−250 mA, %/h, ~18 W, durations) are wrapped with BidiFormatter so they don't reorder inside an Arabic line — the garbling seen before. It's a no-op in LTR locales, so the LTR values are untouched (and the tests stay clean). New labels Now / Average + the %1$s: %2$s line format in EN + AR; the rest reuse the details table's existing strings (Time remaining / Time to full / Temperature / Drain rate). Arabic drafted — pending review.

Data / scope

No new device reads — reuses the same snapshot + rate the tick already computed (#157). No new tracking (the Screen-on/off split stays as #193).

Testing

OngoingStatusLines reworked to 10 tests: collapsed (discharge / charge / no-current-yet), expanded (discharge / charge / drain-rate fallback), the built notification's EXTRA_BIG_TEXT, temperature-only-and-not-expandable when the toggle is off, and the null snapshot. Full :app:testDebugUnitTest (439) + lintDebug green; installed on the Mate 10 Pro.

(Couldn't grab a live shot — the foreground-service notification isn't staying alive under EMUI's background killer — but the Robolectric tests assert the exact posted title and expanded text.)

Closes #194
Related: #192, #193, #173/#188.

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