Native: enable K2 for benchmarks in performance/

Those benchmarks are built with bootstrap KGP and snapshot compiler.
Currently the former is K1, while the latter is K2. As a result, the
build fails because K2 compiler needs -Xfragment-sources argument,
while K1 uses -Xcommon-sources. So KGP passes the latter, while the
compiler expects the former.

Fix this by forcing KGP to use K2 for benchmarks in performance/
This can be reverted once bootstrap is updated to 2.0.0.

kotlin-native/performance/gradle.properties

@@ -18,5 +18,9 @@ artifactoryRepo = kotlin-native-benchmarks
 externalReports = coroutinesReport.txt
 externalBenchmarksReport = externalReport.json
 
+# This can be reverted once bootstrap is updated to 2.0.0:
+kotlin.experimental.tryK2=true
+# See commit message for more details.
+
 # Avoid building platform libraries by the MPP plugin.
 kotlin.native.distribution.type=prebuilt