IR text tests: New tests specifically for main functions mangling

^KT-57755

compiler/testData/ir/irText/declarations/mainFunctionManglingInJvm.kt

@@ -0,0 +1,29 @@
+// TARGET_BACKEND: JVM
+// ^^^ Only JVM allows `main` functions in the same package but in different files.
+
+// FIR_IDENTICAL
+// WITH_STDLIB
+
+// FILE: a.kt
+fun main() {
+    println("main() in a.kt")
+}
+
+// FILE: b.kt
+fun main() {
+    println("main() in b.kt")
+}
+
+// FILE: c.kt
+package foo
+
+fun main() {
+    println("foo.main() in c.kt")
+}
+
+// FILE: d.kt
+package foo
+
+fun main() {
+    println("foo.main() in d.kt")
+}