Do special insert even for custom trimIndent() function to avoid using resolve (KT-31810)

idea/testData/copyPaste/plainTextLiteral/CustomTrimIndent.expected.kt

@@ -0,0 +1,11 @@
+fun String.trimIndent() = this
+
+fun test() = doTest("""
+    def foo(a)
+        a ? 0 : 1
+    end
+""".trimIndent())
+
+fun doTest(rubyCode: String) {
+    // some code here
+}

idea/testData/copyPaste/plainTextLiteral/CustomTrimIndent.kt

@@ -0,0 +1,10 @@
+fun String.trimIndent() = this
+
+fun test() = doTest("""
+    <caret>
+""".trimIndent())
+
+fun doTest(rubyCode: String) {
+    // some code here
+}
+

idea/testData/copyPaste/plainTextLiteral/CustomTrimIndent.txt

@@ -0,0 +1,3 @@
+def foo(a)
+    a ? 0 : 1
+end