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/idea-completion/testData/basic/common/smartCast/functionWithContract.kt

@@ -0,0 +1,15 @@
+// COMPILER_ARGUMENTS: -XXLanguage:+ReadDeserializedContracts -XXLanguage:+UseReturnsEffect
+
+interface Foo {
+    val x: Int
+
+    fun f()
+}
+
+fun test(x: Any?) {
+    require(x is Foo)
+    x.<caret>
+}
+
+// EXIST: x
+// EXIST: f