FIR: add equality call checker

Added checker for FirEqualityOperatorCall. It's surfaced as one of the
following diagnostics depending on the PSI structure and types under
comparison:

* INCOMPATIBLE_TYPES(_WARNING)
* EQUALITY_NOT_APPLICABLE(_WARNING)
* INCOMPATIBLE_ENUM_COMPARISON_ERROR

Comparing with FE1.0, the current implementation is more conservative
and only highlights error if the types are known to follow certain
contracts with `equals` method. Otherwise, the checker reports warnings
instead.

However, the current checker is more strict in the following situations:
1. it now rejects incompatible enum types like `Enum<E1>` and
  `Enum<E2>`, which was previously accepted
2. it now rejects incompatible class types like `Class<String>` and
  `Class<Int>`, which was previously accepted
3. the check now takes smart cast into consideration, so
  `if (x is String) x == 3` is now rejected

compiler/tests-spec/testData/diagnostics/linked/expressions/when-expression/p-6/neg/3.1.fir.kt

@@ -3,8 +3,8 @@
 // TESTCASE NUMBER: 1
 fun case_1(value_1: Int, value_2: TypesProvider): String {
     when (value_1) {
-        -1000L..100 -> return ""
-        value_2.getInt()..getLong() -> return ""
+        <!INCOMPATIBLE_TYPES!>-1000L..100<!> -> return ""
+        <!INCOMPATIBLE_TYPES!>value_2.getInt()..getLong()<!> -> return ""
     }
 
     return ""