[atoms] Fix getText atom for unicode charater middle of word (#8736)

* [atoms] Fix getText atom for unicode charater middle of word

The change to getText atom by commit c065ddaeb6c5cf91ebf797c242128604e38b79e1
does not handle case when unicode character is in the middle
of a word, and unicode character will be incorrectly capitalized
(see https://bugs.chromium.org/p/chromedriver/issues/detail?id=3611).
The problem is \b mark the boundary between word character and
unicode character as a boundary. This is fixed by explicitly using
unicode flag and specifying unicode character and unicode symbol.

* [atoms] Add meta tag for charset in test html

Add charset for utf-8 in text_test.html