Merge pull request #19955 from daviditen/DateTimeCasingRename

Deprecate DateTime methods from issue #18846.

[reviewed by @benharsh]

Deprecate and rename DateTime methods from issue #18846. This has not yet
modified the classes or enums suggested in that issue.

Added a deprecated test to trigger the warnings for each of the deprecated
methods.

Fixed up any tests that were using the now-deprecated names.

modules/packages/TOML.chpl

@@ -1071,9 +1071,9 @@ used to recursively hold tables and respective values
         when fieldReal do return val.re:string;
         when fieldString do return ('"' + val.s + '"');
         when fieldEmpty do return ""; // empty
-        when fieldDate do return val.ld.isoformat();
-        when fieldTime do return val.ti.isoformat();
-        when fieldDateTime do return val.dt.isoformat();
+        when fieldDate do return val.ld.isoFormat();
+        when fieldTime do return val.ti.isoFormat();
+        when fieldDateTime do return val.dt.isoFormat();
         otherwise {
           throw new owned TomlError("Error in printing " + val.s);
           return val.s;