[llvm] [APFloat][NFCI] Move x87DoubleExtended next to the other native IEEE types (PR #223193)

[Eric Ross via llvm-commits]

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ZERICO2005 wrote:

One could also argue that `float` and `double` are more common than `half` and `bfloat`, and should be tested first.

https://github.com/llvm/llvm-project/pull/223193