Refactor the code to not be dependant on day.js

[DevVali]

Task: Use built-in JavaScript functions to calculate the date. As this is just a refactor of the code, it should perform just as with day.js. Changing the structure is fine, although the structure can remain as is. Here is the unfinished snippet I have:

const vscode = require('vscode');
const dayjs = require('dayjs');
const { yourXmas } = vscode.workspace.getConfiguration('xmasTime');

// Helpers

/**
 * @param {string} targetDate
 * @returns {{ ms: number, days: number, hours: number, minutes: number}}
 */
function getDifference(targetDate) {
    // ...

    return {
        ms: diffMs,
        days: diffDays,
        hours: diffHours,
        minutes: diffMinutes,
    };
}

function getUnit(difference) {
    // ...
}

// Get the time left and return the text

function getTimeLeft() {
    // ...
}

module.exports = { getTimeLeft };

[DevVali]

Make sure to work on this issue in the se2-v2 branch!