fix(cli): scope Android template's keepDebugSymbols to the debug build type only

[2akouwu]

Root cause

The generated app/build.gradle.kts in the mobile Android template wrote:

buildTypes {
    getByName("debug") {
        ...
        packaging {
            jniLibs.keepDebugSymbols.add("*/arm64-v8a/*.so")
            ...
        }
    }

AGP's Kotlin BuildType DSL (com.android.build.api.dsl.ApplicationBuildType) has no packaging member. Because Kotlin resolves an unmatched receiver against the next enclosing scope, that packaging { ... } call silently binds to the outer android {} extension's packaging property instead of anything debug-specific. The keep-symbols globs therefore applied to every build type, including release:

1. Release .so files shipped unstripped, since AGP's stripReleaseDebugSymbols task matched the glob and copied the lib verbatim instead of running llvm-strip.
2. ndk.debugSymbolLevel produced no debug-symbols bundle metadata, because ExtractNativeDebugMetadataTask compares byte lengths against the (no-op) strip output and sees them as already stripped.

Both failures are silent — no warning or error is emitted anywhere in the build.

Why this fix

I used the fix the issue itself verified working (AGP 8.11.0 / Gradle 8.14.3): move the keep-symbols globs out of the buildTypes DSL entirely and apply them through the variant API, which is the only surface that actually scopes a setting to a single build type:

androidComponents {
    onVariants(selector().withBuildType("debug")) { variant ->
        variant.packaging.jniLibs.keepDebugSymbols.add("*/arm64-v8a/*.so")
        ...
    }
}

I considered instead moving the packaging {} call to sit next to compileOptions/buildFeatures inside android {} with some kind of build-type conditional, but the DSL doesn't offer a clean way to conditionally scope glob entries there without re-implementing what androidComponents.onVariants already does — so the variant-API approach is both the smallest change and the technically correct one. I kept the existing {{#each abi-list}} Handlebars loop as-is, just changed the surrounding Kotlin scaffolding, to keep the diff minimal.

The issue also names a second affected template in cargo-mobile2 (templates/platforms/android-studio/app/build.gradle.kts.hbs), but that file lives in the separate tauri-apps/cargo-mobile2 repository and isn't part of this repo, so it's out of scope here.

Testing

Added debug_keep_debug_symbols_is_not_applied_to_every_build_type in crates/tauri-cli/src/mobile/android/project.rs, which loads the real (unrendered) template via include_str! and asserts:

• the getByName("debug") { ... } block (up to getByName("release")) no longer contains a packaging block, guarding against this mis-scoping regressing, and
• an androidComponents { ... } block exists that scopes to selector().withBuildType("debug") and contains keepDebugSymbols.

This test fails against the pre-fix template (where packaging/keepDebugSymbols sit inside the debug build type and no androidComponents block exists) and passes with the fix applied. I did not run cargo test in this environment since it requires network access to fetch crate dependencies that isn't available here, but the test only does string slicing/contains checks against a &'static str produced by include_str!, so it doesn't depend on any Android/Gradle toolchain — I traced the logic by hand against both the old and new template content to confirm the assertions land as expected on each.

Fixes #15884.