PROPOSAL: Use 400 weight for H1 and H2, fall back to sans-serif for Simplified and Traditional Chinese headings

[johnzhou721]

[Test URL: https://beewareorg--10.org.readthedocs.build/zh-cn/10/]

The Chinese rendering for headings right now has very thin characters as compared to the english characters in Cutive:

This is due to the fact that the default MkDocs theme wants H2 to be 300 weight, but Cutive does not have that thin of a weight, so it falls back onto the regular font weight, which is very thick for a "Regular" or 300 font. Since not only Chinese but other non-Cutive fonts is likely to have this problem, I've bumped the weight for H1 and H2 to 400.

In addition, the serifs looks out of place in Chinese because the style (Songti / Mingti; I don't know which one) doesn't match the slab-serif style of Cutive. Sans-Serif matches better, so I've added a variable for Chinese to use sans-serif in headings as well.

@freakboy3742 @kattni I'm interested in hearing thoughts on this change. For reference, sans-serif Chinese with 400 weight:

Serif Chinese with 400 weight:

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[kattni]

@johnzhou721 PR #150 is part of the website migration. As it affects all the documentation, and there is a change in the header, we are waiting to take it live until the new website is live. In that PR, I have gone to great lengths to disable the dynamic font sizing in the MkDocs Material theme. This means that every header font size is defined explicitly in rem. I understand where you're going with this, but with everything in flux, this is not the time to make this change. I'm converting this to a draft so it doesn't get merged by someone else who doesn't have the context. When we take things live, please test your issues against that setup, and we can discuss it at that point if needed.

[johnzhou721]

@kattni Sorry, I apologize for not seeing the conflict with #150. And also I meant to mark this as draft, as I labeled it PROPOSAL, but I somehow clicked the wrong button. This also affects the tutorial, and I apologize for neglecting to concern that as part of the website migration there was also a Docs Tools PR.