Fix decompiler tests.

For now, JVM and JS backends produce different metadata for package facades (and package parts),
and thus different output is expected for JVM and JS decompiler.
Split decompiler tests into common (decompiledText), JVM-specific (decompiledTextJvm),
and JS-specific (decompiledTextJs)
Join them back together if JS backend migrates to JVM-like package model.

idea/testData/decompiler/decompiledTextJs/TestPackage.expected.kt

@@ -0,0 +1,12 @@
+// IntelliJ API Decompiler stub source generated from a class file
+// Implementation of methods is not available
+
+package test
+
+private var i: kotlin.Int /* compiled code */
+
+internal val p: kotlin.Int /* compiled code */
+
+internal fun f(): kotlin.Unit { /* compiled code */ }
+
+internal fun kotlin.Int.plus(i: kotlin.Int /* = compiled code */): kotlin.Int { /* compiled code */ }

idea/testData/decompiler/decompiledTextJs/TestPackage/TestPackage.kt

@@ -0,0 +1,10 @@
+package test
+
+fun f() {}
+val p = 3
+private var i = 2
+
+fun Int.plus(i: Int = 1) = this + i
+
+class ShouldNotBeVisible1
+interface ShouldNotBeVisible2