Switch kotlin version to 1.8

with appropriate fixes in testdata, tests and other
places.

compiler/testData/diagnostics/tests/smartCasts/loops/elvisIfBreakInsideWhileTrue.fir.kt

@@ -1,9 +0,0 @@
-public fun foo(x: String?, y: String?): Int {
-    while (true) {
-        x ?: <!INVALID_IF_AS_EXPRESSION!>if<!> (y == null) break
-        // y is nullable if x != null
-        y<!UNSAFE_CALL!>.<!>length
-    }
-    // y is null because of the break
-    return y<!UNSAFE_CALL!>.<!>length
-}

compiler/testData/diagnostics/tests/smartCasts/loops/elvisIfBreakInsideWhileTrue.kt

@@ -1,6 +1,7 @@
+// FIR_IDENTICAL
 public fun foo(x: String?, y: String?): Int {
     while (true) {
-        x ?: <!INVALID_IF_AS_EXPRESSION_WARNING!>if<!> (y == null) break
+        x ?: <!INVALID_IF_AS_EXPRESSION!>if<!> (y == null) break
         // y is nullable if x != null
         y<!UNSAFE_CALL!>.<!>length
     }