[3.12] gh-108269: Add CFBundleAllowMixedLocalizations to Info.plist on macOS (GH-113213) (#113294)

gh-108269: Add CFBundleAllowMixedLocalizations to Info.plist on macOS (GH-113213)

Adding this key with a value of true enables detecting the
users prefered language in libraries accessing system APIs
for this.
(cherry picked from commit 4cfce3a4da7ca9513e7f2c8ec94d50f8bddfa41b)

Co-authored-by: Ronald Oussoren <ronaldoussoren@mac.com>