Add lang specific font stacks for CJK

[CL-Jeremy]

Summary of potential ameliorations to go-gitea#6007, based on my knowledge, updated today to match this branch):

• Contrary to some misinformation on the Web, inherit only works alone and not in a sequence, and font is no exception, they are removed (for monospace I can rely on browser choice locally, works at least on macOS and Linux, on Safari and Firefox, but we may as well try to introduce an override mixin just like normal fonts).
• Actually fixing the font chooser (elements with an explicit lang property definition should be rendered based on that).
• Searching for parts of the current fallback sequence, I realized Microsoft YaHei New it is widely used but I could not find any source for that name, at least that doesn't match anything on any of my test environments. Microsoft JhengHei New doesn't even exist.
• Hiragino Sans TC is not available unless otherwise purchased, but I tend to leave it there to match the widely accepted Hiragino Sans GB, notably shipped with macOS for over 10 years and used on various Mainland Chinese websites.
• SF Mono is available since macOS High Sierra and is currently used on GitHub.
• Regarding the non-English name matching, I do not suggest blindly including them unless English names error out during testing. I suspect those were needed for legacy Windows platform/browser combinations which are barely supported anyway.
• A widely adopted approach of "fixing" Yu Gothic being too thin at regular weight on Windows is included (Microsoft JhengHei is about as thin, but that is reasonable given the nature of traditional Chinese characters, while Japanese Kanjis are normally not as complex).
• As already stated in Add lang specific font stacks for CJK go-gitea/gitea#6007 (comment), Helvetica should precede Arial (the latter is shipped with macOS since more than 10 years ago); some may argue the problem of hinting on Windows at lower resolutions (as with Hiragino Sans), but since their presence on the affected platforms are due to the user's manual installation they are responsible for their own choice.
• The Hong Kong regional variants of PingFang, Source Han Sans and PMingLiU and are prioritized accordingly.
• Single and double quotes are normalized, and unnecessary ones are removed.

This PR has been tested against the master branch with merge conflicts resolve. Pending discussions affecting this include:

1. Whether Lato should be abandoned in favor of the native fonts
2. If not 1, whether and how Lato should be updated to include the latest glyphs of Latin-Extended and Cyrillic code blocks from official.
3. Whether the compiled and minified stylesheets should be left to the build script and ignored in development trees.