Allow languages to define multiple folding.markers

[mjbvz]

It seems that languages can currently only define a single folder.marker. I'd like to be able to define two or more of these if possible. For example, in some languages it would make sense to support both comment and #pragma regions.

Probably falls under the scope of #3422

[aeschli]

You can define multiple pattern like here

[mjbvz]

Makes sense. One case I was also thinking about was how you could use this to define markdown heading foldings. I imagine this would use a bunch of rules like:

// h1 folding
{
   start: #\s*\w+,
   end: #{1}\s*\w+
}

h2 folding
{
   start: ##\s*\w+,
   end: #{1,2}\s*\w+
}

...

to ensure each heading level would consume all subheadings

[aeschli]

IMO that's better done through language aware folding. Regexes have their limitations and can get very expensive.
Closing as dup of #3422