Use withFramework instead of legacy API

[wallymathieu]

Description

Use CreateProcess API in order to be able to use withFramework to fix behavior on *nix systems.

• This will fixes Fsc.compileExternal documentation suggests possible to use with exe #2395

Added a String.splitLines in order to split error string into lines.

TODO

Feel free to open the PR and ask for help

• Does TimeSpan.MaxValue need to be passed along to create process?

• unit or integration test exists (or short reasoning why it doesn't make sense)

  Note: Consider using the CreateProcess API which can be tested more easily, see https://github.com/fsharp/FAKE/pull/2131/files#diff-4fb4a77e110fbbe8210205dfe022389b for an example (the changes in the DotNet.Testing.NUnit module)

• boy scout rule: "leave the code behind in a better state than you found it" (fix warnings, obsolete members or code-style in the places you worked in)

• Fake 5 API guideline is honored

[wallymathieu]

Does this look OK @matthid ?

[matthid]

Generally, the change is OK. I think instead of "fixing" the new public API an alternative would be to "inline" the function as private function into Fake.DotNet.Fsc if you don't want to go down the other way

[matthid]

Any interest in adding a test for the change? (it will take a bit for me to get everything green again anyway)

[matthid]

Please also merge release/next in order to get a green build

[wallymathieu]

I'll try to find time to add some tests