Of course, almost immediately after posting a question I've stumbled upon a solution. This issue comments (https://github.com/Microsoft/vscode/issues/15058) gave me a hint, so I tried cursorMove command with "to": "viewPortTop" and "to": "viewPortBottom" arguments and, surprisingly, it worked.
The complete json to be added to keybindings.json is:
{
"key": "ctrl+pageup",
"command": "cursorMove",
"when": "editorTextFocus",
"args": {
"to": "viewPortTop"
}
} ,
{
"key": "ctrl+pagedown",
"command": "cursorMove",
"when": "editorTextFocus",
"args": {
"to": "viewPortBottom"
}
}
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…