Fixed mixup with keycode / modifier mapping.

Keycode mapping and modifier mapping were done through the same function
and same map, and this caused a conflict where KEYCODE_1 was being
mapped as META_FN_ON. I've separated these two methods

Test: ShortcutHelperCategoriesRepositoryTest
Flag: com.android.systemui.keyboard_shortcut_helper_rewrite
Fix: 372820099
Change-Id: If67ec7919d8dd24c519d5e4d64bd988cb9a07cf6