Scripting: support scripts starting with UTF-8 BOM

#KT-54705 fixed

libraries/tools/kotlin-main-kts-test/test/org/jetbrains/kotlin/mainKts/test/mainKtsIT.kt

@@ -154,6 +154,13 @@ class MainKtsIT {
             listOf("""\{"firstName":"James","lastName":"Bond"\}""", "User\\(firstName=James, lastName=Bond\\)")
         )
     }
+
+    @Test
+    fun testUtf8Bom() {
+        val scriptPath = "$TEST_DATA_ROOT/utf8bom.main.kts"
+        Assert.assertTrue("Expect file '$scriptPath' to start with UTF-8 BOM", File(scriptPath).readText().startsWith(UTF8_BOM))
+        runWithKotlincAndMainKts(scriptPath, listOf("Hello world"))
+    }
 }
 
 fun runWithKotlincAndMainKts(
@@ -204,3 +211,5 @@ fun runWithK2JVMCompilerAndMainKts(
     }
 }
 
+internal const val UTF8_BOM = 0xfeff.toChar().toString()
+

libraries/tools/kotlin-main-kts-test/test/org/jetbrains/kotlin/mainKts/test/mainKtsTest.kt

@@ -266,6 +266,14 @@ class MainKtsTest {
         )
     }
 
+    @Test
+    fun testUtf8Bom() {
+        val scriptPath = "$TEST_DATA_ROOT/utf8bom.main.kts"
+        Assert.assertTrue("Expect file '$scriptPath' to start with UTF-8 BOM", File(scriptPath).readText().startsWith(UTF8_BOM))
+        val res = evalFile(File(scriptPath))
+        assertSucceeded(res)
+    }
+
     private fun assertSucceeded(res: ResultWithDiagnostics<EvaluationResult>) {
         Assert.assertTrue(
             "test failed:\n  ${res.reports.joinToString("\n  ") { it.severity.name + ": " + it.message + if (it.exception == null) "" else ": ${it.exception}" }}",

libraries/tools/kotlin-main-kts-test/testData/utf8bom.main.kts

@@ -0,0 +1 @@
+println("Hello world")