[JS IR] Add to IR keep possibility similar to legacy-dce one

It helps to:

- keep declarations even if they are not reachable and not exported
- not minify names of not exported declarations

Compiler argument: -Xir-keep=A,B

Can be used for top-level declarations or for member

^KT-54118 fixed

js/js.translator/testData/box/keep/keepOverriddenMethod.kt

@@ -0,0 +1,38 @@
+// TARGET_BACKEND: JS_IR
+// ONLY_IR_DCE
+// RUN_PLAIN_BOX_FUNCTION
+// INFER_MAIN_MODULE
+// KEEP: A.foo
+
+// MODULE: keep_overridden_method
+// FILE: lib.kt
+
+open class A {
+    open fun foo(): String {
+        return "foo"
+    }
+
+    open fun bar(): String {
+        return "bar"
+    }
+}
+
+open class B : A() {
+    override fun foo(): String {
+        return super.foo() + "!"
+    }
+}
+
+@JsExport
+fun bar(): B {
+    return B()
+}
+
+// FILE: test.js
+function box() {
+    var b = this["keep_overridden_method"].bar()
+
+    if (b.foo_26di_k$() != "foo!") return "fail 1"
+
+    return "OK"
+}