test: port libvterm unit test to neovim test suite

These were imported from the v0.3.3 git tag
https://github.com/neovim/libvterm/tree/v0.3.3 and not the latest
commit. This is for compatibility reasons as the libvterm code was
imported from v0.3.3.

test/unit/testutil.lua

@@ -151,6 +151,13 @@ local function filter_complex_blocks(body)
         or string.find(line, 'mach_vm_range_recipe')
       )
     then
+      -- HACK: remove bitfields from specific structs as luajit can't seem to handle them.
+      if line:find('struct VTermState') then
+        line = string.gsub(line, 'state : 8;', 'state;')
+      end
+      if line:find('VTermStringFragment') then
+        line = string.gsub(line, 'size_t.*len : 30;', 'size_t len;')
+      end
       result[#result + 1] = line
     end
   end