[FE] Make dynamic a suitable resulted type

This fixes a FIR-specific issue where a type variable is inferred to
Any instead of dynamic. K1 wasn't affected because of a FIR-specific
condition in ResultTypeResolver.

#KT-57962 Fixed

compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/setOperatorOnDynamic.fir.kt

@@ -0,0 +1,13 @@
+// FIR_DUMP
+// DIAGNOSTICS: -UNUSED_ANONYMOUS_PARAMETER, -UNUSED_VARIABLE
+
+fun foo() {
+    val x1: Any = arrayOf<String>().fold("") { res, key ->
+        res.length
+        <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.String")!>res<!>
+    }
+    val x3: Any = arrayOf<String>().fold(js("({})")) { res, key ->
+        res[key] = "hello"
+        <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Nothing..kotlin.Any?!")!>res<!>
+    }
+}

compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/setOperatorOnDynamic.fir.txt

@@ -0,0 +1,13 @@
+FILE: setOperatorOnDynamic.fir.kt
+    public final fun foo(): R|kotlin/Unit| {
+        lval x1: R|kotlin/Any| = R|kotlin/arrayOf|<R|kotlin/String|>().R|kotlin/collections/fold|<R|kotlin/String|, R|kotlin/String|>(String(), <L> = fold@fun <anonymous>(res: R|kotlin/String|, key: R|kotlin/String|): R|kotlin/String| <inline=Inline, kind=UNKNOWN>  {
+            R|<local>/res|.R|kotlin/String.length|
+            ^ R|<local>/res|
+        }
+        )
+        lval x3: R|kotlin/Any| = R|kotlin/arrayOf|<R|kotlin/String|>().R|kotlin/collections/fold|<R|kotlin/String|, R|dynamic|>(R|kotlin/js/js|(String(({}))), <L> = fold@fun <anonymous>(res: R|dynamic|, key: R|kotlin/String|): R|dynamic| <inline=Inline, kind=UNKNOWN>  {
+            R|<local>/res|.R|<dynamic>/set|(vararg(R|<local>/key|, String(hello)))
+            ^ R|<local>/res|
+        }
+        )
+    }

compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/setOperatorOnDynamic.kt

@@ -0,0 +1,13 @@
+// FIR_DUMP
+// DIAGNOSTICS: -UNUSED_ANONYMOUS_PARAMETER, -UNUSED_VARIABLE
+
+fun foo() {
+    val x1: Any = arrayOf<String>().fold("") { res, key ->
+        res.length
+        <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.String")!>res<!>
+    }
+    val x3: Any = arrayOf<String>().fold(js("({})")) { res, key ->
+        res[key] = "hello"
+        <!DEBUG_INFO_EXPRESSION_TYPE("dynamic")!>res<!>
+    }
+}