Update DateTimeUtils#parse to support date strings

[kqarryzada]

Updated the DateTimeUtils class to allow evaluation of date strings without a timestamp, e.g., "1970-01-01". Although this is not generally used in SCIM, it broadens compatibility in certain cases, such as if a date is provided in a SCIM filter without a timestamp. Date strings will be given a timestamp marking the beginning of the day.

This does incur a small performance penalty for identifying invalid date strings. However, this tradeoff is worthwhile to provide a slightly more useful parsing implementation. In general, most invocations are expected to provide a valid string, and that primary path is unaffected.

Reviewer: dougbulkley
Reviewer: vyhhuang

JiraIssue: DS-51859

[kqarryzada]

I removed these since timezones don't get the useful "Invalid value for..." message that matches the regex in the test above.

[kqarryzada]

These were already supported, but now there is a dedicated regression test.

[vyhhuang]

These changes look good to me.

[dougbulkley]

Claude suggests these additions into the datesWithoutTimestamps data provider, I'll leave it up to you to implement or not:

        // RFC 7643 states that "A date time... has no case sensitivity".
        // This should also apply to the date-only fallback parsing path.
        { "1970-01-01z", 0L, UTC },

        // Non-zero-minute offsets, to match the variety already covered
        // for full timestamps in 'timestampTestCases'.
        { "1970-01-01+05:30", -19800000L, zone(5, 30) },
        { "1970-01-01-09:30", 34200000L, zone(-9, -30) },

        // An explicit "+00:00" offset should be equivalent to "Z".
        { "1970-01-01+00:00", 0L, UTC },

[kqarryzada]

Claude suggests these additions into the datesWithoutTimestamps data provider

Thanks Doug. I don't anticipate a strong need to support these edge cases if we ever update the parser, so I'll forgo this for the time being.