Crash in plugin: variant.generateBuildConfigProvider.get() returns null with buildFeatures.buildConfig = false on AGP 8.0+

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**Describe the bug**
The Gradle plugin throws a `NullPointerException` when trying to access `variant.generateBuildConfigProvider.get().versionCode.getOrNull()` in modules where `buildConfig` is disabled.

---

**Stacktrace**

```
Cannot invoke method get() on null object
> saveSDKVersionTask.sdkVersionCode = variant.generateBuildConfigProvider.get().versionCode.getOrNull()
```

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**Root cause**
Starting with **AGP 8.0**, `variant.generateBuildConfigProvider` may be `null` if `buildFeatures.buildConfig = false` is explicitly set in the module’s `build.gradle`. This causes the `.get()` call to crash.

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**How to reproduce**

1. Set `buildFeatures.buildConfig = false` in a module's `build.gradle(.kts)`
2. Run the build
3. Observe the crash when the plugin accesses `generateBuildConfigProvider`

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**Expected behavior**
The plugin should check whether `generateBuildConfigProvider` is `null` before accessing it, or avoid relying on this API if it's deprecated.

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**Environment**

* AGP version: 8.7.1
* Gradle: 8.8
* Android Studio: 2024.2.1 (Ladybug)
* Plugin version: last

---

**Suggested fix**
Replace:

```kotlin
saveSDKVersionTask.sdkVersionCode = variant.generateBuildConfigProvider.get().versionCode.getOrNull()
```

With a safe fallback:

```kotlin
variant.generateBuildConfigProvider?.get()?.versionCode?.getOrNull()?.let {
saveSDKVersionTask.sdkVersionCode = it
}
```

Or extract the versionCode from `defaultConfig` if possible.

Search the plugin code for the saveSDKVersionTask assignment involving variant.generateBuildConfigProvider and inspect how buildFeatures.buildConfig is handled. Reproduce with buildConfig disabled using the reported AGP and Gradle versions, then verify the build completes without the null crash and SDK version persistence remains correct.

Written by the indexing model from the issue text.