Enable JSON negative indexing for Oracle 21c+ using [last-N]

[Clifford Gama]

Follow up to #36085 which added negative indexing for sqlite (as a new feature for 6.0).

While doing some reading on JSON queries on Oracle, I found that you ​can index elements from the right by using [last-N].

An array index can also have the form last - N, where - is a minus sign (hyphen) and N is a literal whole number (0, 1, 2,…) that is no greater than the array size minus 1. The next-to-last array element can be referenced using index last-1, the second-to-last by index last-2, and so on. Whitespace surrounding the minus sign (hyphen) is ignored.

I think we can use this to support negative indexing on Oracle versions that support [last-N]. Currently, trying to do so raises a NotSupportedError per #36085 which was focused on sqlite.

I can't find Oracle release notes specifying when [last-N] indexing was added, but the note I quoted is only available in 21c+ docs.

[Jacob Walls]

Thanks Clifford. Leaving as a "feature" since we should document, but not punting to new-features since there is a bugfix aspect, as we shouldn't be raising NotSupportedError for behavior that the database supports but we just haven't implemented.

[GitHub <noreply@…>]

In 7e4c4f4:

Fixed #36718 -- Added JSONField support for negative array indexing on Oracle 21c+.