[FIR] Introduce a feature flag for context-sensitive enum resolution

The feature was previously enabled unconditionally in K2 which
triggered a bug when an enum has an entry with the same name as itself.

#KT-58897 Fixed
#KT-52774

compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// KT-58897
+
+enum class A {
+    A,
+    B,
+}
+
+fun test2(a: A) = when (a) {
+    A.A -> "A"
+    A.B -> "B"
+}