feat: Add `region` code fold support & test files

[TheCyberRonin]

If this PR is accepted, it will add support for code folding using regions and test files associated with different region possibilities.

Code folding is really nice using regions and I use it all the time. I noticed that this language server didn't have it and saw that it was fairly easy to add support for it.

The test files show the different ways that a region can start and end in both of the supported file formats.

As far as usefulness, you can turn this chunk of code:

-------------------------------
-- palettes
-------------------------------

function init_palettes()
 local a=0x5d00
 for p=0,15 do
  for c=0,15 do
   poke(a,bor(sget(p,c),c==14 and 0x80))
   a+=1
  end
 end
end

function set_palette(no,off)
 memcpy(off or 0x5f00,
  0x5d00+shl(flr(no),4),
  16)
end

To this:

-- #region palettes

function init_palettes()
 local a=0x5d00
 for p=0,15 do
  for c=0,15 do
   poke(a,bor(sget(p,c),c==14 and 0x80))
   a+=1
  end
 end
end

function set_palette(no,off)
 memcpy(off or 0x5f00,
  0x5d00+shl(flr(no),4),
  16)
end
-- #endregion

The second would allow you to fold the code in between the region comments so you can hide it and worry about the stuff you want to.

[TheCyberRonin]

Glad that I could add something useful!