Mastodon: hashtag's link text range is incorrect in the Web UI

[mayaeh]

After #8447 has been merged, it seems incorrect processing of hashtags including multibyte characters such as the following in WebUI.
https://taruntarun.net/@mayaeh/101557400350655981.json
It recognized the entire "testテスト" as a hashtag, but "テスト" does not become a link.

However, it seems to be no problem with a hashtag composed only of multibyte characters.

Expected behaviour

I think it should be as follows:
https://edge.taruntarun.net/@mayaeh/101557496224395192

Actual behaviour

https://taruntarun.net/@mayaeh/101557400350655981

Steps to reproduce the problem

Post a hashtag combining single byte alphanumeric characters and multibyte characters.

Specifications

Equivalent to master branch

[hinaloe]

Here is a simple sample spec.
https://github.com/hinaloe/mastodon/commit/e2cb63c9933fbddd85db7635c6dd1d9030211337