This is a reland of c1226cea1ec11d5b766226c912c475647a731274

Original change's description:
> [scanner] Simplify TemplateSpan raw literal character handling
> 
> Instead of adding and removing literal chars, only add raw literal characters when we have to and never remove them.
> 
> Change-Id: Ib604c8c9fb69a96708eec3a03de102e0668c01d7
> Reviewed-on: https://chromium-review.googlesource.com/1167505
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Caitlin Potter <caitp@igalia.com>
> Commit-Queue: Toon Verwaest <verwaest@chromium.org>

Change-Id: Ia15501d75c3beaf336e90a80e0abb738f696ef9e
Reviewed-on: https://chromium-review.googlesource.com/1170604Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55040}