[Gradle, JS] IR by default and report warnings for using legacy compiler

- just legacy - report warning about deprecation
- both - report warning about deprecation of legacy
- no compiler explicitly chosen - error about explicit setting compiler

warn from cli legacy compiler

nowarn flag - kotlin.js.compiler.nowarn

KT-42326
KT-53074

compiler/testData/cli/js/modulesWithSameNames.args

@@ -1,9 +1,11 @@
 $TESTDATA_DIR$/separateModules/sepModule1.kt
+-Xlegacy-deprecated-no-warn
 -meta-info
 -output
 $TEMP_DIR$/m1/m.js
 ---
 $TESTDATA_DIR$/separateModules/sepModule2.kt
+-Xlegacy-deprecated-no-warn
 -libraries
 $TEMP_DIR$/m1
 -output