Merge tyUncheckedArray with tySeq in typeRel (#23866)

Ref https://github.com/nim-lang/Nim/issues/23836#issuecomment-2233957324

Their types are basically equivalent so they should behave the same way
for type relations.

compiler/sigmatch.nim

@@ -1305,11 +1305,6 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
       else:
         if lengthOrd(c.c.config, fRange) != lengthOrd(c.c.config, aRange):
           result = isNone
-  of tyUncheckedArray:
-    if a.kind == tyUncheckedArray:
-      result = typeRel(c, elementType(f), elementType(a), flags)
-      if result < isGeneric: result = isNone
-    else: discard
   of tyOpenArray, tyVarargs:
     # varargs[untyped] is special too but handled earlier. So we only need to
     # handle varargs[typed]:
@@ -1350,9 +1345,8 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
             typeRel(c, base(f), base(a), flags) >= isGeneric:
           result = isConvertible
     else: discard
-  of tySequence:
-    case a.kind
-    of tySequence:
+  of tySequence, tyUncheckedArray:
+    if a.kind == f.kind:
       if (f[0].kind != tyGenericParam) and (a.elementType.kind == tyEmpty):
         result = isSubtype
       else:
@@ -1367,8 +1361,8 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
             result = isSubtype
           else:
             result = isNone
-    of tyNil: result = isNone
-    else: discard
+    elif a.kind == tyNil:
+      result = isNone
   of tyOrdinal:
     if isOrdinalType(a):
       var x = if a.kind == tyOrdinal: a.elementType else: a

tests/typerel/tuncheckedarray_eq.nim

@@ -0,0 +1,2 @@
+type p = ptr UncheckedArray[char]
+doAssert p is ptr UncheckedArray