FIR: Rework receivers processing in resolution

- Put extensionReceiver to candidate even if it's explicit (for sake of clarity)
- Split CheckReceiver (dispatch part should only check nullability)

compiler/testData/diagnostics/tests/declarationChecks/localVariablesWithTypeParameters_1_3.fir.kt

@@ -11,7 +11,7 @@ fun test() {
     const val <T> a3 = 0
     <!INAPPLICABLE_LATEINIT_MODIFIER!>lateinit val <T> a4 = 0<!>
     val <T> a5 by Delegate<Int>()
-    val <T> a6 by Delegate<<!UNRESOLVED_REFERENCE!>T<!>>()
+    val <T> a6 by <!INAPPLICABLE_CANDIDATE!>Delegate<<!UNRESOLVED_REFERENCE!>T<!>>()<!>
 }
 
 class Delegate<F> {

compiler/testData/diagnostics/tests/declarationChecks/localVariablesWithTypeParameters_1_4.fir.kt

@@ -11,7 +11,7 @@ fun test() {
     const val <T> a3 = 0
     <!INAPPLICABLE_LATEINIT_MODIFIER!>lateinit val <T> a4 = 0<!>
     val <T> a5 by Delegate<Int>()
-    val <T> a6 by Delegate<<!UNRESOLVED_REFERENCE!>T<!>>()
+    val <T> a6 by <!INAPPLICABLE_CANDIDATE!>Delegate<<!UNRESOLVED_REFERENCE!>T<!>>()<!>
 }
 
 class Delegate<F> {