Report flag use-fir in Gradle statistics

#KT-49633 Fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/compilerRunner/GradleKotlinCompilerRunner.kt

@@ -152,6 +152,7 @@ internal open class GradleCompilerRunner(
                         report(BooleanMetrics.JVM_COMPILER_IR_MODE, args.useIR)
                         report(StringMetrics.JVM_DEFAULTS, args.jvmDefault)
                         report(StringMetrics.USE_OLD_BACKEND, args.useOldBackend.toString())
+                        report(StringMetrics.USE_FIR, args.useFir.toString())
                     }
                 }
                 is K2JSCompilerArguments -> {

libraries/tools/kotlin-gradle-statistics/src/org/jetbrains/kotlin/statistics/metrics/StringMetrics.kt

@@ -47,6 +47,7 @@ enum class StringMetrics(val type: StringOverridePolicy, val anonymization: Stri
     // Compiler parameters
     JVM_DEFAULTS(CONCAT, SAFE),
     USE_OLD_BACKEND(CONCAT, SAFE),
+    USE_FIR(CONCAT, SAFE),
 
     JS_PROPERTY_LAZY_INITIALIZATION(CONCAT, SAFE),
 }