Try to map non-character KeySyms to VKEYs taking into account active modifiers,

Try to map non-character KeySyms to VKEYs taking into account active modifiers,
before trying to map with the modifier states stripped from the event. This is
required for keyboard layouts which have non-character functions accessed via a
modifier to a key that normally generates a character, e.g. the AltGr+D
combination of the "Neo" layout, which has the "D" key generate VKEY_DOWN rather
than VKEY_D.

Character KeySyms are still mapped with modifier state stripped, so that e.g.
Ctrl+D generates VK_CONTROL followed by VKEY_D.

BUG=408034,421304
TEST=Verified on linux_chromeos.

Review URL: https://codereview.chromium.org/629243002

Cr-Commit-Position: refs/heads/master@{#298909}