Change policy with legacy compiler backend

[JS] Remove incremental js jps test

[JS] Remove test of maven js archetype

[JS] Fix another one test

[JS] Fix tests for jps

[JS] Try to fix maven test data

[JS] Fix test data

[JS] Fix test data for ant

[JS] Fix jsExtraHelp test

[JS] Fix test run from not-Gradle build tools

[JS] Set flag without compiler error

[JS] Disable warnings and errors in legacy compiler called from Gradle

[JS] Proofread messages

[JS] Not proofread messages

KT-42326

compiler/testData/integration/ant/js/manySources/build.log.expected

@@ -3,7 +3,14 @@ Buildfile: [TestData]/build.xml
 
 build:
 [kotlin2js] Compiling [[TestData]/root1, [TestData]/bar.kt, [TestData]/root2/Foo.kt] => [[Temp]/out.js]
-[kotlin2js] warning: legacy compiler is deprecated. Please migrate onto IR.
+[kotlin2js] warning: ==========
+[kotlin2js] This project currently uses the Kotlin/JS Legacy compiler backend, which has been deprecated and will be removed in a future release.
+[kotlin2js]
+[kotlin2js] Please migrate your project to the new IR-based compiler (https://kotl.in/jsir).
+[kotlin2js] Because your build tool will not support the new Kotlin/JS compiler, you will also need to migrate to Gradle.
+[kotlin2js]
+[kotlin2js] You can continue to use the deprecated legacy compiler in the current version of the toolchain by providing the compiler option -Xuse-deprecated-legacy-compiler.
+[kotlin2js] ==========
 
 BUILD SUCCESSFUL
 Total time: [time]

compiler/testData/integration/ant/js/manySources/build.xml

@@ -9,6 +9,7 @@
            <include name="**/*.kt"/>
          </fileset>
        </src>
+      <compilerarg value="-Xuse-deprecated-legacy-compiler"/>
     </kotlin2js>
   </target>
 </project>