Fix PR ada/111813 (Inconsistent limit in Ada.Calendar.Formatting)

Fix PR ada/111813 (Inconsistent limit in Ada.Calendar.Formatting)

The description of the second Value function (returning Duration) (ARM 9.6.1(87)
doesn't place any limitation on the Elapsed_Time parameter's value, beyond
"Constraint_Error is raised if the string is not formatted as described for Image, or
the function cannot interpret the given string as a Duration value".

It would seem reasonable that Value and Image should be consistent, in that any
string produced by Image should be accepted by Value. Since Image must produce
a two-digit representation of the Hours, there's an implication that its
Elapsed_Time parameter should be less than 100.0 hours (the ARM merely says
that in that case the result is implementation-defined).

The current implementation of Value raises Constraint_Error if the Elapsed_Time
parameter is greater than or equal to 24 hours.

This patch removes the restriction, so that the Elapsed_Time parameter must only
be less than 100.0 hours.

2023-10-15 Simon Wright <simon@pushface.org>

	PR ada/111813
gcc/ada/
	* libgnat/a-calfor.adb (Value (2)): Allow values of
	parameter Elapsed_Time greater than or equal to 24 hours, by doing
	the hour calculations in Natural rather than Hour_Number (0 ..
	23). Calculate the result directly rather than by using Seconds_Of
	(whose Hour parameter is of type Hour_Number).
	If an exception occurs of type Constraint_Error, re-raise it
	rather than raising a new CE.

gcc/testsuite/
	* gnat.dg/calendar_format_value.adb: New test.