Switch Latexify interface to use LaTeX strings instead of expressions

[isaacsas]

Currently the Latex interface tries to generate Exprs to pass to Latexify via the recipes. This results in Symbolics being limited by how Latexify chooses to convert an expression into a Latex string (and any bugs that might be present there). A more flexible approach would be to use latexraw to generate strings within the Symbolics recipes, as this would allow Symbolics to then easily post-process the generated strings to customize display (and make it easier to have user-provided customization options).

[isaacsas]

It is also inconsistent, as sometimes Symbolics generates strings and sometimes it generates Exprs as in https://github.com/JuliaSymbolics/Symbolics.jl/blob/60a414e633c6abead5ad0367359f8a5f1da1cca5/src/latexify_recipes.jl#L18-L55

[ChrisRackauckas]

Yes it would be nice to just make latex strings.