Updated dependencies to yew 0.21 and gloo 0.10

[mibes404]

Description

Updated the dependencies to yew 0.21 and gloo 0.10

This pull request consists of the following changes:

• Cargo.toml files updated to yew 0.21 and gloo 0.10
• Function signatures to match the new format of yew 0.21
• collect_text_content() and assert_empty_children() functions to make the code compile

Checklist

• I have self-reviewed and tested this pull request to my best ability.
• I have added tests for my changes.
• I have updated docs to reflect any new features / changes in this pull request.
• I have added my changes to CHANGELOG.md.

[futursolo]

Could you please also update the changelog to indicate that the next version will be compatible with Yew v0.21.0?

[mibes404]

Sure. I've updated the CHANGELOG.
Based on the fact that the release is not backwards compatible with Yew 0.20, I've assumed you want to bump the release to 0.9.

[futursolo]

Thank you!

I will publish the next release shortly.