Use new Kotlin/JS plugin

[turansky]

Part of #1938

[elizarov]

Look good to me. Note, that the new Kotlin/JS has build-in Webpack support and it should be possible to completely get rid of the custom node configuration in gradle/node-js.gradle.

[skuzmich]

Thanks for the PR! This is one step closer to enabling JS IR build of this example.

Please add

diff --git a/js/example-frontend-js/npm/webpack.config.js b/js/example-frontend-js/npm/webpack.config.js
index a208d047..8428c557 100644
--- a/js/example-frontend-js/npm/webpack.config.js
+++ b/js/example-frontend-js/npm/webpack.config.js
@@ -38,6 +38,7 @@ module.exports = {
     resolve: {
         modules: [
             path.resolve(__dirname, "kotlin-js-min/main"),
+            path.resolve(__dirname, "kotlin-js-min/legacy/main"),
             path.resolve(__dirname, "../src/main/web/")
         ]
     },

as this place is changed in 1.4-M1 with kotlin.js.compiler=both property. Can be tested it with -Pkotlin_version=1.4-M1 -Patomicfu_version=0.14.2-1.4-M1 -Phtml_version=0.7.1-build-1707 and a @file:Suppress("NO_EXPLICIT_VISIBILITY_IN_API_MODE")

Otherwise looks good to me.

[turansky]

Next 2 steps after this PR:

1. Use new MPP plugin for core
2. Use build/distributions in examples
   2.1. Remove old DCE

@skuzmich Could I skip your change request in this case (CR will be removed in step 2)?

[turansky]

Note, that the new Kotlin/JS has build-in Webpack support and it should be possible to completely get rid of the custom node configuration in gradle/node-js.gradle.

One of the goal of this PR - simplify migration to Kotlin DSL (no gradle/node-js.gradle == no migration required)

gradle/test-mocha-js.gradle also in "remove list"

[skuzmich]

If kotlinx.coroutines maintainers are OK with temporarily breaking 1.4 builds in one more place, I can lift the change request.
cc @elizarov