Improve language selection experience in code block elements

[cloverich]

The current code block language select added in #175 is rudimentary, a basic dropdown. Ideally it would have the following behaviors:

• Look nicer
• Use typeahead
• Automatically default to previous language, or infer language (vs plaintext by default)
• Sort recent languages to top, in an obvious way (because remainder are alphabetical)
• Remove or hide rarely used languages (ANTLR, etc). Consider making languages configurable (reduces bundle size)
• Allow setting a default language in preferences (perhaps: default language, or "last used", or "sort X languages to top", etc)

Plate's examples use radix dropdown and a fully custom select menu, but wanted to evaluate other proper select menu's, and probably do #129 before sinking time into this feature.