Currently, to use a promise from C++ we either have to use an ASM block
(which does not work well with dynamic linking) or declare exports in
the EMSCRIPTEN_BINDINGS block, which is cumbersome and cannot be chained.
This solution makes it easy to use js promises by introducing the
WebPromiseManager which dispatches callbacks to appropriate callers when
available.
This is a preliminary patch for FileSystem support, which will heavily
use async APIs.
Task-number: QTBUG-99611
Change-Id: I368a8f173027eaa883a9ca18d0ea6a3e99b86071
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
d0eba2449a