Wasm backend ghci browser mode

This patch implements wasm backend ghci browser mode support. Under the ghci browser mode, all Haskell code runs in the browser main thread, JSFFI interacts with the browser context instead of nodejs, allowing the user to do frontend live-coding via ghci. All ghci functionalities that already works in ghci nodejs mode shall also work with browser mode, including the ghci debugger. Closes #25399 (closed).

Current status: Done in the sense that it works on my machine. Works with Firefox/Chrome. Remaining items:

• Test in CI (needs ci-images!163 (merged), landed)
• User manual
• More comments
• More descriptive commit messages