[FIR] add vararg arguments support, improve vararg parameters support

compiler/testData/codegen/box/arrays/arrayInstanceOf.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 //test [], get and iterator calls
 fun test(createIntNotLong: Boolean): String {
     val a = if (createIntNotLong) IntArray(5) else LongArray(5)

compiler/testData/codegen/box/arrays/kt4348.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 operator fun String.get(vararg value: Any) : String {
     return if (value[0] == 44 && value[1] == "example") "OK" else "fail"
 }

compiler/testData/codegen/box/arrays/kt4357.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun box(): String {
     val array = intArrayOf(11, 12, 13)
     val p = array.get(0)

compiler/testData/codegen/box/arrays/kt503.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // IGNORE_BACKEND: JS_IR
 // TODO: muted automatically, investigate should it be ran for JS or not
 // IGNORE_BACKEND: JS

compiler/testData/codegen/box/arrays/kt7288.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun test(b: Boolean): String {
     val a = if (b) IntArray(5) else LongArray(5)
     if (a is IntArray) {

compiler/testData/codegen/box/arrays/kt7338.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // IGNORE_BACKEND: NATIVE
 // IGNORE_BACKEND: JS_IR
 // TODO: muted automatically, investigate should it be ran for JS or not

compiler/testData/codegen/box/arrays/varargsWithJava.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM
 // FILE: AT.java