This integration test fails intermittently because we're not
(correctly) awaiting the sandbox actions. The `27R` field in
`issue14862.pdf` triggers sandbox events for every typing action, but
for the backspace and "a" character typing actions we weren't awaiting
the sandbox trip at all, and for other places we weren't awaiting it
fully (causing some characters to be missed in the assertion).
This commit fixes the issues by using the appropriate helper functions,
similar to what we did in PR #18399. Not only is this shorter in terms
of code, but it also fixed the near-permafail for this test with newer
versions of Puppeteer.
3adf8b6be0