Support contracts in PartialBodyResolveFilter

Previously, PartialBodyResolveFilter didn't know about contracts and was
filtering out calls of such functions, leading to unstable completion in
cases like that:

fun test(x: Any?) {
    require(x is String)
    x.<caret>
}

However, PartialBodyResolveFilter works by pure PSI, while to determine
if function has a contract we have to resolve it.

To solve it, we do something very similar to what has been done with
Nothin-returning functions: introduce
KotlinProbablyContractedFunctionShortNameIndex, which collects all
function which *may* have a contract during indexing.

^KT-25275 Fixed

idea/testData/resolve/partialBodyResolve/DeclarationsBefore.completion

@@ -9,7 +9,10 @@ fun foo(p: Int) {
         val v2 = v1 * v1
         val v3 = v1 * v2
 
-        /* STATEMENT DELETED: run { val v2 = 1 println(v2) } */
+        run {
+            val v2 = 1
+            println(v2)
+        }
 
         print(<caret>v2)