feat(android): add WebP image format + fix uncompressed PNG output

[PrestaEdit]

Add WebP output for Android bitmap resources + fix uncompressed PNGs

Motivation

Google Play Console flags apps that ship large, unoptimized bitmap resources under
"Optimize your app's images". On a real production app (Alys, com.prestaedit.alys)
the 5 splash-density PNGs alone weighed ~24 MB in the AAB — enough to trigger
the warning by themselves. Two root causes:

1. resizePng() in Concerns/InstallsAppIcon.php calls imagepng($resized, $dst, 0) — compression level 0, i.e. essentially uncompressed. A 1280×1920 splash lands at 9.4 MB instead of ~2 MB. Icons pay the same tax.
2. Android supports WebP natively at aapt level since API 14 (lossless: API 18). NativePHP's minSdk sits well above that in every real-world project. Emitting WebP shrinks the same splash to ~1 MB losslessly — same visual output, ~90% smaller.

Together these are Google's #1 bitmap-optimization suggestion in Play Console.

Changes

Config — config/nativephp.php gets a new opt-in toggle:

'android' => [
    // ...
    'image_format' => env('NATIVEPHP_ANDROID_IMAGE_FORMAT', 'png'),
],

Default 'png' keeps behavior identical for existing projects (zero BC break).
Set 'webp' (or NATIVEPHP_ANDROID_IMAGE_FORMAT=webp in .env) to opt in.

Concerns/InstallsAppIcon.php

• Rename resizePng() → resizeImage(), add $format parameter ('png'|'webp').
• imagepng($dst, 0) → imagepng($dst, 9) — max compression. Applies to both PNG and WebP branches and shrinks PNG icons/splashes by 60-70% on its own (this is arguably a bug fix that could stand alone).
• Add imagewebp($dst, IMG_WEBP_LOSSLESS) branch.
• New readImage() helper reads either PNG or WebP source (uses imagecreatefromwebp when available).
• New androidImageFormat() helper reads the config and gracefully falls back to 'png' if PHP GD was compiled without WebP support (imagewebp not available).
• installAndroidIcon(): destination filename now derived from $format, and any stale opposite-extension file in the same folder is deleted first (avoids AAPT duplicate-resource errors on repeated builds when the toggle changes).

Concerns/InstallsAndroidSplashScreen.php

• Detect public/splash.webp / public/splash-dark.webp in addition to .png (WebP wins when both exist).
• Output filename becomes splash.{png,webp} following the config.
• Same stale-file cleanup before writing.
• validateSplashImage() accepts WebP sources too.

Backwards compatibility

• Default 'png' — no change for existing projects.
• Even when a project opts into 'webp', if the host's PHP GD was built without WebP support (imagewebp missing), androidImageFormat() transparently downgrades to 'png' rather than crash the build.
• Renaming the private helper (resizePng → resizeImage) has no external surface — both traits/concerns are consumed together via PreparesBuild.

Impact (real data from a shipping app)

Before (default settings today):

drawable-xxxhdpi/splash.png  9.4 MB
drawable-xxhdpi/splash.png   5.3 MB
drawable-xhdpi/splash.png    2.4 MB
drawable-hdpi/splash.png     1.3 MB
drawable-mdpi/splash.png     0.6 MB
                            ------
                            19.0 MB per theme × 2 themes = ~38 MB

After, image_format=png (just the compression fix):

Same set: ~10-12 MB per theme (60-70% smaller)

After, image_format=webp (lossless):

drawable-xxxhdpi/splash.webp  0.9 MB
drawable-xxhdpi/splash.webp   0.5 MB
drawable-xhdpi/splash.webp    0.3 MB
drawable-hdpi/splash.webp    0.15 MB
drawable-mdpi/splash.webp    0.07 MB
                            ------
                            ~1.9 MB per theme × 2 = ~3.8 MB

~34 MB shaved off the AAB, Play Console's bitmap warning cleared.

Test plan

• Existing test suite (InstallsAndroidSplashScreenTest, InstallsAndroidTest) still passes with default config.
• Add coverage for image_format=webp code path.
• Add coverage for .webp source detection.
• Manual: build a sample app with NATIVEPHP_ANDROID_IMAGE_FORMAT=webp, unzip the AAB, verify drawable-*/splash.webp present and drawable-*/splash.png absent; run app, splash renders correctly.
• Manual: build the same app on a PHP install without WebP support in GD (rare) — should silently fall back to PNG output.

Related

Play Console → App → Overview → "4 recommended actions" → "Improve your app's performance with bitmap image optimization".