minor improvements to follow up recent PRs (#20342)

put mOpenArrayToSeq in compile-time evaluation whitelist
(it was mNone before which was whitelisted), homogenize
"ordinal type expected" errors, put overloadable enums
in non-experimental manual

doc/manual_experimental.md

@@ -86,44 +86,6 @@ No Unicode normalization step is performed.
   pragma `{.experimental: "unicodeOperators".}` reliably.
 
 
-Overloadable enum value names
-=============================
-
-Enum value names are overloadable, much like routines. If both of the enums
-`T` and `U` have a member named `foo`, then the identifier `foo` corresponds
-to a choice between `T.foo` and `U.foo`. During overload resolution,
-the correct type of `foo` is decided from the context. If the type of `foo` is
-ambiguous, a static error will be produced.
-
-  ```nim  test = "nim c $1"
-
-  type
-    E1 = enum
-      value1,
-      value2
-    E2 = enum
-      value1,
-      value2 = 4
-
-  const
-    Lookuptable = [
-      E1.value1: "1",
-      # no need to qualify value2, known to be E1.value2
-      value2: "2"
-    ]
-
-  proc p(e: E1) =
-    # disambiguation in 'case' statements:
-    case e
-    of value1: echo "A"
-    of value2: echo "B"
-
-  p value2
-  ```
-
-Previously required `{.experimental: "overloadableEnums".}` to enable,
-now always enabled.
-
 Top-down type inference
 =======================