Show source code for builtin function in the UI

[pbiggar]

trafficstars

It's useful to users to expose the definition of built-in functions.

If we add a filename and line number to the definition of builtin functions (hopefully using builtin F# features), we could link directly to the code in question (we also have the server's build-hash).

If we also added an ending line number, we could pull in the source code directly from the GitHub raw file.

Phases:

• add filename, starting line number, and ending line number to all stdlib definition
• send these to the client
• use the client to build a link to the function
• parse the github webpage to read the source code
• add a syntax highlighting library.

Or is it simpler to pre-process the dark F# codebase to produce a JSON file of F# code, that we can then put in a CDN?

[StachuDotNet]

Copied from duplicate, now-closed #3704:

We should provide users with whatever info they need, and this is sometimes useful information. It also helps users become familiar with our GitHub and the fact that they could contribute.

[StachuDotNet]

Rather than encoding this within our F# backend, this could encourage a GitHub API package, with which we:

• fetch all files of pattern Lib*.fs
• extract the fn defs from there, and use that data to support this feature

May be a non-traditional or roundabout approach, but one that we could support wholly from within Dark.

[StachuDotNet]

merged into #5237