FIR2IR: declare receivers for all accessors of extension properties

Before this commit, extension receivers were declared only for
properties with container source, which is strange & inconsistent.
Now we declare accessor extension receiver iff corresponding property
has extension receiver.

compiler/testData/ir/irText/declarations/extensionProperties.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 val String.test1 get() = 42
 
 var String.test2