Given a Date value, return a new Date representing the first day of the same month and year. The day component is always 1.
Examples:
Input: d = Date.newInstance(2024, 6, 15)
Output: Date.newInstance(2024, 6, 1)
Explanation: Returns the first day of June 2024
Input: d = Date.newInstance(2024, 1, 31)
Output: Date.newInstance(2024, 1, 1)
Explanation: Returns the first day of January 2024
Input: d = Date.newInstance(2024, 12, 25)
Output: Date.newInstance(2024, 12, 1)
Explanation: Returns the first day of December 2024
Input: d = Date.newInstance(2024, 2, 29)
Output: Date.newInstance(2024, 2, 1)
Explanation: Returns the first day of February 2024 (leap year)
Input: d = Date.newInstance(2023, 11, 1)
Output: Date.newInstance(2023, 11, 1)
Explanation: Already the first day of the month, returns the same date
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