Speed up JS IR BE tests compiling the common parts (runtime + test common utils) once (on demand) and sharing the result between tests

It's a temporary hack until we implement IR based library format.
It relies on the fact that currently, IR BE generates stable (enough) names.​

compiler/testData/codegen/box/delegation/hiddenSuperOverrideIn1.0.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND: JVM_IR
 // LANGUAGE_VERSION: 1.0
 

compiler/testData/codegen/box/ieee754/nullableDoubleEquals10.kt

@@ -1,5 +1,4 @@
 // LANGUAGE_VERSION: 1.0
-// IGNORE_BACKEND: JS_IR
 fun myEquals(a: Double?, b: Double?) = a == b
 
 fun myEquals1(a: Double?, b: Double) = a == b

compiler/testData/codegen/box/ieee754/nullableDoubleNotEquals10.kt

@@ -1,5 +1,4 @@
 // LANGUAGE_VERSION: 1.0
-// IGNORE_BACKEND: JS_IR
 fun myNotEquals(a: Double?, b: Double?) = a != b
 
 fun myNotEquals1(a: Double?, b: Double) = a != b

compiler/testData/codegen/box/ieee754/nullableFloatEquals10.kt

@@ -1,5 +1,4 @@
 // LANGUAGE_VERSION: 1.0
-// IGNORE_BACKEND: JS_IR
 fun myEquals(a: Float?, b: Float?) = a == b
 
 fun myEquals1(a: Float?, b: Float) = a == b

compiler/testData/codegen/box/ieee754/nullableFloatNotEquals10.kt

@@ -1,5 +1,4 @@
 // LANGUAGE_VERSION: 1.0
-// IGNORE_BACKEND: JS_IR
 fun myNotEquals(a: Float?, b: Float?) = a != b
 
 fun myNotEquals1(a: Float?, b: Float) = a != b

compiler/testData/codegen/box/ieee754/whenNullableSmartCast10.kt

@@ -1,5 +1,4 @@
 // LANGUAGE_VERSION: 1.0
-// IGNORE_BACKEND: JS_IR
 fun box(): String {
     val nullValue: Any? = null
     val nullDouble: Double? = null