[Build] Use -Xuse-k2 flag instead of -Xuse-fir

buildSrc/src/main/kotlin/common-configuration.gradle.kts

@@ -163,7 +163,7 @@ fun Project.configureKotlinCompilationOptions() {
                 freeCompilerArgs += jvmCompilerArgs
 
                 if (useJvmFir && project.path !in projectsWithDisabledFirBootstrap) {
-                    freeCompilerArgs += "-Xuse-fir"
+                    freeCompilerArgs += "-Xuse-k2"
                     freeCompilerArgs += "-Xabi-stability=stable"
                     if (useFirLT) {
                         freeCompilerArgs += "-Xuse-fir-lt"

libraries/commonConfiguration.gradle

@@ -60,7 +60,7 @@ ext.configureFrontendIr = { Project project ->
     project.tasks.withType(KotlinCompile.class) { task ->
         task.kotlinOptions {
             if (project.kotlinBuildProperties.useFirForLibraries) {
-                freeCompilerArgs += "-Xuse-fir"
+                freeCompilerArgs += "-Xuse-k2"
                 allWarningsAsErrors = false
             }
             if (project.properties.renderDiagnosticNames) {