Issue #216 & #240 - add order by support of multiple fields, ASC/DESC and NULLS FIRST/LAST & fix to ensure recalc when order by field changes

[jondavis9898]

I followed the preference (#223 (comment)) to leave the order by at the RollupSummaryField level rather than move it to the Context level and believe this provides as much backwards compat as possible.

The only place I could not provide 100% backwards compat is on the public member variable detailOrderBy in RollupSummaryField which changed from a Schema.DescribeField to a List<LREngine.Ordering>. It does not appear that the order by additions made in DLRS previously have made their way over to the LREngine project so this change would only effect internal DLRS usage (which I've handled in this PR) and anyone using the library source (and directly accessing this member) instead of as a package.

With all that said, I think it's worth discussing moving the order by to the context level for a couple of reasons. I'll open a new issue to explain in more detail.

[jondavis9898]

Please see comments in PR #241 before merging this PR.

Note

• If the decision is made to NOT implement Concatenation Rollups order maybe none Deterministic - Consider moving order by from LREngine.RollupSummaryField to LREngine.Context #239, then PR Issue #216 & #240 - add order by support of multiple fields, ASC/DESC and NULLS FIRST/LAST & fix to ensure recalc when order by field changes #238 should be merged and PR Issue #216, #239 & #240 - add order by support of multiple fields, ASC/DESC and NULLS FIRST/LAST; move orderby to context; fix to ensure recalc when order by field changes #241 cancelled.
• If the decision is made to implement Concatenation Rollups order maybe none Deterministic - Consider moving order by from LREngine.RollupSummaryField to LREngine.Context #239, then PR Issue #216, #239 & #240 - add order by support of multiple fields, ASC/DESC and NULLS FIRST/LAST; move orderby to context; fix to ensure recalc when order by field changes #241 should be merged and PR Issue #216 & #240 - add order by support of multiple fields, ASC/DESC and NULLS FIRST/LAST & fix to ensure recalc when order by field changes #238 cancelled.

[jondavis9898]

Please see comments in #239 (comment) prior to merging this PR.

Only 1 of the following PRs should be merged: #238, #241, #243, #244