ext/standard: Sync parameter names for fpow() to be identical to pow()

[Girgias]

I don't know how this did not get caught before, but I found this out while writing the docs for fpow().
It should follow the same, more descriptive, parameter names of the pow() functions.

This needs RM approval, but I would hope this is uncontroversial @php/release-managers-84

[SakiTakamachi]

Since this is a new feature, there is no BC.
I support this because considering the named arguments thing, this is probably our last chance to fix it safely.

[Girgias]

I will let CI run, and merge it if it is Green

[NattyNarwhal]

looks cosmetic, I agree shouldn't cause any problems