fix(web): apply correct key codes to scan codes mapping (#866)

The root cause of the bug is the incorrect keycodes-to-scancodes
mappings. These mappings translated the browser's key codes (like
"KeyA") to OS-specific scancode (OS where the browser runs). However,
that's not exactly what we need to do. We need to map the browser's key
codes to _Windows_ scancodes - the only format that is accepted by _VNC_
and _RDP_) modules.
Let's look at an example for a better understanding. _Safari_ browser
used _Linux_'s _Gecko) mappings as a fallback (because there were no
MacOS-specific mappings). For a given key, _iron-remote-desktop_ was
providing a scancode that did not correspond to the _Windows_ scancode
for that same key. As a result, the `IronVNC` module incorrectly mapped
this scancode to a `KeySym`, which resulted in an incorrect `KeySym` or
`NO_SYMBOL`.

Author: RRRadicalEdward