[JS IR] Perform optimizations on the generated JS code

The patch adopts and reuses the optimizations from the legacy backend.

The optimizations remove useless temporary variables,
statements and simplify generated JS code.

The optimizations can be disabled by `-Xoptimize-generated-js=false`.

Related to KT-51139

compiler/testData/debug/stepping/lambdaStepInlineWithDefaults.kt

@@ -30,8 +30,4 @@ fun box(): String {
 // test.kt:16 box
 
 // EXPECTATIONS JS_IR
-// test.kt:2 box
-// test.kt:3 box
-// test.kt:7 box
-// test.kt:10 box
 // test.kt:16 box