rename RealField/RealNumber

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As part of ticket #24457 we perform the following class renaming
- `RealField` -> `RealFloatingPointField_factory`
- `RealField_class` -> `RealFloatingPointField`
- `RealNumber` -> `RealFloatingPoint`

Component: **basic arithmetic**

_Issue created by migration from https://trac.sagemath.org/ticket/24524_

