Implement methods for LogExpFunctions

[theogf]

Fixes #931

This adds LogExpFunctions as an explicit dependency (already was an implicit one).

For each function where it would error on Num values, a new specialized method was added.

[ChrisRackauckas]

@ArnoStrouwen did you look into https://github.com/JuliaSymbolics/Symbolics.jl/actions/runs/6458255398/job/17531947753?pr=993#step:5:10 before?

[ArnoStrouwen]

@ArnoStrouwen did you look into https://github.com/JuliaSymbolics/Symbolics.jl/actions/runs/6458255398/job/17531947753?pr=993#step:5:10 before?

Yes, mathengine is passed wrongly to makedocs instead of Documenter.HTML.
Bracket closed to early.
Fix should be included here:
#978