[Wasm] Loader improvements

- Output ES modules instead of plain files
- Support -Xwasm-launcher=d8 for d8 shell used in tests and benchmarks.
- Reuse launcher generation logic in CLI and box tests runners.
- Create separate output directory for each box since
  there are multiple output files generated for each test.
- Stop using absolute paths in generate JS files
  to simplify running generated code on different machine
- Remove ">>>" from println output


Merge-request: KT-MR-5729
Merged-by: Svyatoslav Kuzmich <svyatoslav.kuzmich@jetbrains.com>

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.kt

@@ -242,7 +242,7 @@ class K2JSCompilerArguments : CommonCompilerArguments() {
 
     @Argument(
             value = "-Xwasm-launcher",
-            valueDescription = "esm|nodejs",
+            valueDescription = "esm|nodejs|d8",
             description = "Picks flavor for the wasm launcher. Default is ESM."
     )
     var wasmLauncher: String? by NullableStringFreezableVar("esm")