[FIR] Render k2-specific flexible types in a more compact way in diagnostic messages

^KT-62031 fixed

compiler/fir/analysis-tests/testData/resolve/flexibleTypeRendering.fir.txt

@@ -0,0 +1,4 @@
+FILE: main.kt
+    public final fun foo(p: R|AAA<kotlin/String>|, s: R|kotlin/Int?|): R|kotlin/Unit| {
+        R|<local>/p|.R|SubstitutionOverride</AAA.process: R|kotlin/Unit|><Inapplicable(INAPPLICABLE): /AAA.process>#|<<ERROR TYPE REF: Cannot infer argument for type parameter Q>>(R|<local>/s|)
+    }

compiler/fir/analysis-tests/testData/resolve/flexibleTypeRendering.kt

@@ -1,7 +1,7 @@
 // FILE: main.kt
 
 fun foo(p: AAA<String>, s: Int?) {
-    p.process(<!ARGUMENT_TYPE_MISMATCH("ft<Q & Any, Q?>; kotlin.Int?")!>s<!>)
+    p.process(<!ARGUMENT_TYPE_MISMATCH("Q!; kotlin.Int?")!>s<!>)
 }
 
 // FILE: AAA.java