[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/sourceMapRelativeRoot.args

@@ -1,10 +1,12 @@
 $TESTDATA_DIR$/sourceMapRelativeRoot/lib/src/lib.kt
+-Xlegacy-deprecated-no-warn
 -source-map
 -meta-info
 -output
 $TESTDATA_DIR$/sourceMapRelativeRoot/lib/out/lib.js
 ---
 $TESTDATA_DIR$/sourceMapRelativeRoot/main/src/main.kt
+-Xlegacy-deprecated-no-warn
 -libraries
 $TESTDATA_DIR$/sourceMapRelativeRoot/lib/out/
 -source-map