Convert editing/selection/modify_move/move-by-word-visually-multi-space.html with selection_test

This patch converts the web test with selection_test() so that the test
cases are more explicit and the expectations are easier to maintain.

This is a preparation for switching to logical left/right caret movement:
crrev.com/c/1593632

Bug: 958831
Change-Id: Icab3b62cbce61333d0a4dd72650b17dc9dda2494
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594808
Auto-Submit: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657204}
88 files changed