[ts] Typecheck settings/KeybindsSettingsTab.js with TypeScript
[ts] Typecheck settings/KeybindsSettingsTab.js with TypeScript

Bug: chromium:1011811
Change-Id: I344168e2117ef4e1c22cb27ef3a235ad8c182642
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2495770
Reviewed-by: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>
Commit-Queue: Andres Olivares <9d3bededfc9b98cb289557338a8f98e77d597607@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend