Handle 'T' separator in wxDateTime::ParseDateTime()

ParseDateTime() currently fails if there is a 'T' separator in front of
time component. FormatISOCombined() uses this separator as the default,
so wxDateTime can't parse its own formatted results by default.

This commit fixes that issue by allowing an optional 'T' between the
date and time parts.

Closes #22999.

src/common/datetimefmt.cpp

@@ -1753,6 +1753,10 @@ wxDateTime::ParseDateTime(const wxString& date, wxString::const_iterator *end)
         while ( endDate != date.end() && wxIsspace(*endDate) )
             ++endDate;
 
+        // Skip possible 'T' separator in front of time component
+        if ( endDate != date.end() && *endDate == 'T' )
+            ++endDate;
+
         const wxString timestr(endDate, date.end());
         if ( !dtTime.ParseTime(timestr, &endTime) )
             return false;

tests/datetime/datetimetest.cpp

@@ -1440,6 +1440,15 @@ void DateTimeTestCase::TestDateTimeParse()
             false
         },
 
+        {
+            // with 'T' separator
+            "2010-01-04T14:30",
+            {  4, wxDateTime::Jan, 2010, 14, 30,  0 },
+            true,
+            "",
+            false
+        },
+
         {
             // date after time
             "14:30:00 2020-01-04",