Intent to unship: Recursive call of Document.execCommand()

`Document.execCommand()` may cause firing DOM events and/or running some observers. Therefore, web apps can call it recursively. However, Chromium has already stopped supporting it (since 2014)[1][2]. And it'll be documented in execCommand spec[3]. This is testing in Nightly and early Beta[4

Intent to Unship: Recursive call of Document.execCommand() (Only Nightly and early Beta for now)

`Document.execCommand()` may cause firing DOM events and/or running some observers. Therefore, web apps can call it recursively. However, Chromium has already stopped supporting it: https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/renderer/core/editing/commands/docu