fix(select): wire DROPDOWN_BUILTIN_PLACEMENTS into AsyncSelect

Mirrors the static Select wrapper so AsyncSelect dropdowns keep the
#36963 fix (disabled horizontal viewport adjustment) after the antd v6
upgrade, instead of falling back to antd's default placements.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: rusackas

superset-frontend/packages/superset-ui-core/src/components/Select/AsyncSelect.tsx

@@ -86,6 +86,7 @@ import {
   MAX_TAG_COUNT,
   TOKEN_SEPARATORS,
   DEFAULT_SORT_COMPARATOR,
+  DROPDOWN_BUILTIN_PLACEMENTS,
 } from './constants';
 
 const Error = ({ error }: { error: string }) => (
@@ -791,6 +792,7 @@ const AsyncSelect = forwardRef(
           placeholder={placeholder}
           showSearch={shouldShowSearch}
           tokenSeparators={tokenSeparators}
+          builtinPlacements={DROPDOWN_BUILTIN_PLACEMENTS}
           value={selectValue}
           suffixIcon={getSuffixIcon(
             isLoading,