Bug 1094031 - Let LayoutManager._updateCurrentPage() use LayoutNormalizer._normalizeKey()

- Extract a new class LayoutKeyNormalizer from LayoutNormalizer, which can be used by LayoutNormalizer and LayoutManager.
Merge pull request #26274 from mnjul/bug_1094031_use_normalier_in_layout_manager

Bug 1094031 - Let LayoutManager._updateCurrentPage() use LayoutNormalizer._normalizeKey(). r=timdream