Ensure nested ordered identifiers are grouped (fixes #745)

[john-bodley]

Fixes https://github.com/andialbrecht/sqlparse/issues/745.

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (f101546) 96.97% compared to head (d43fb9c) 96.98%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #746 +/- ## ======================================= Coverage 96.97% 96.98% ======================================= Files 20 20 Lines 1556 1557 +1 ======================================= + Hits 1509 1510 +1 Misses 47 47 ``` | [Files](https://app.codecov.io/gh/andialbrecht/sqlparse/pull/746?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andi+Albrecht) | Coverage Δ | | |---|---|---| | [sqlparse/engine/grouping.py](https://app.codecov.io/gh/andialbrecht/sqlparse/pull/746?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andi+Albrecht#diff-c3FscGFyc2UvZW5naW5lL2dyb3VwaW5nLnB5) | `100.00% <100.00%> (ø)` | |

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[andialbrecht]

Ah, cool! Thanks for finding this!