[5.2] CalendarField: changing strftime to date

[Hackwar]

Pull Request for Issue #42790 and a lot more.

Summary of Changes

When using the calendar field without a format and without setting translateformat="true", the field tries to convert the value with strftime(), which is deprecated and throws a warning. This PR replaces strftime() with date() instead and converts the time format from strftime to date-format. To make this as compatible as possible, the conversion method has been extended to include as many conversions as possible. Since this only converts datetimes, the chance that someone is using a format with additional text besides the strftime-format is neglectable.

Testing Instructions

Actual result BEFORE applying this Pull Request

Expected result AFTER applying this Pull Request

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[ceford]

Can you give us exact test instructions? I have forgotten what happened previously and I cannot reproduce the error in 5.2.0-beta3-dev.

[richard67]

Can you give us exact test instructions? I have forgotten what happened previously and I cannot reproduce the error in 5.2.0-beta3-dev.

@ceford Maybe it can be tested as described in PR #43947 ? I haven't tried that yet.

[chmst]

I get the message only with PHP < 8.2. The patch works as described for this field, but did not test with other configurations. and not sure if this is a good solution.

Field definition in my component.

	<field
		name="date_from"
		type="calendar"
		format="%Y-%m-%d"
		showtime="false"
		label="COM_EVENT_DATE_FROM"
		description="COM_EVENT_DATE_FROM_DESC"
	/>

@ceford for a test, change the field definiton in a compoment, for example in com_content, article.xml like this or with all possible different settings:

		<field
			name="created"
			type="calendar"
			label="COM_CONTENT_FIELD_CREATED_LABEL"
		format="%Y-%m-%d"
		showtime="false"
			filter="user_utc"
		/>

and different php versions