Binding "tab" key

I see here https://www.scintilla.org/ScintillaDoc.html#KeyBindings that tab is available as `SCK_TAB` but it can't be assigned to a shortcut `npp.AddShortcut` or using this:

```
function func1(ch)
if (ch == " ") then
print("Doesn't work (this message is never shown).");
end

print("Typed a regular character like a, b, c, d, e, etc... works.")
end

npp.AddEventHandler("OnChar", func1)
```

If I assign it manually in Notepad++'s settings then it works but the default action of `[tab]` becomes disabled (so I can't make indentation then).

Is there a way to detect `[tab]` so that I could insert text after it's pressed with `editor:AddText("text");`?

Start with the OnChar event handling, npp.AddShortcut, and editor:AddText("text") usage shown in the issue, then compare their tab-key behavior with Scintilla's SCK_TAB documentation. Done means determining whether a script can detect Tab without disabling default indentation and documenting or exposing a working way to insert text after the key is pressed.

由索引模型根据 Issue 内容生成。