[FIR] Improved lambda completion: initial implementation

Repeat the logic of KotlinConstraintSystemCompleter in ConstraintSystemCompleter.
Implement additional context operations required for updated lambda completion algorithm.

compiler/testData/diagnostics/tests/resolve/specialConstructions/inferenceForElvis.fir.kt

@@ -4,5 +4,5 @@
 fun <T: Any> foo(f: (T) -> Unit): T? = null // T is used only as return type
 fun test() {
     val x = foo { it checkType { _<String>() }} ?: "" // foo() is inferred as foo<String>, which isn't very good
-    val y: Any = foo { <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.String")!>it<!> checkType { <!INAPPLICABLE_CANDIDATE!>_<!><Any>() } } ?: "" // but for now it's fixed by specifying expected type
+    val y: Any = foo { <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any")!>it<!> checkType { _<Any>() } } ?: "" // but for now it's fixed by specifying expected type
 }