Remove Gradle Isolated Project violation

Calls to Project.properties is not Gradle Isolated Projects safe as it
causes Gradle to look through parent projects to find these. Move to
using providers.gradleProperty as that does not have the same behavior.

Test: ./gradlew build --dry-run -Dorg.gradle.unsafe.isolated-projects=true
      fewer warnings after the PR

build-logic/convention/src/main/kotlin/com/google/samples/apps/nowinandroid/KotlinAndroid.kt

@@ -23,7 +23,6 @@ import org.gradle.api.plugins.JavaPluginExtension
 import org.gradle.kotlin.dsl.assign
 import org.gradle.kotlin.dsl.configure
 import org.gradle.kotlin.dsl.dependencies
-import org.gradle.kotlin.dsl.provideDelegate
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 import org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension
 import org.jetbrains.kotlin.gradle.dsl.KotlinBaseExtension
@@ -78,14 +77,16 @@ internal fun Project.configureKotlinJvm() {
 private inline fun <reified T : KotlinBaseExtension> Project.configureKotlin() = configure<T> {
     // Treat all Kotlin warnings as errors (disabled by default)
     // Override by setting warningsAsErrors=true in your ~/.gradle/gradle.properties
-    val warningsAsErrors: String? by project
+    val warningsAsErrors = providers.gradleProperty("warningsAsErrors").map {
+        it.toBoolean()
+    }.orElse(false)
     when (this) {
         is KotlinAndroidProjectExtension -> compilerOptions
         is KotlinJvmProjectExtension -> compilerOptions
         else -> TODO("Unsupported project extension $this ${T::class}")
     }.apply {
         jvmTarget = JvmTarget.JVM_11
-        allWarningsAsErrors = warningsAsErrors.toBoolean()
+        allWarningsAsErrors = warningsAsErrors
         freeCompilerArgs.add(
             // Enable experimental coroutines APIs, including Flow
             "-opt-in=kotlinx.coroutines.ExperimentalCoroutinesApi",