fix(live_grep/grep_string): support non-utf8 patterns (#2570)

lua/telescope/builtin/__files.lua

@@ -126,6 +126,10 @@ files.live_grep = function(opts)
     end
   end
 
+  if opts.file_encoding then
+    additional_args[#additional_args + 1] = "--encoding=" .. opts.file_encoding
+  end
+
   local args = flatten { vimgrep_arguments, additional_args }
   opts.__inverted, opts.__matches = opts_contain_invert(args)
 
@@ -187,6 +191,10 @@ files.grep_string = function(opts)
     end
   end
 
+  if opts.file_encoding then
+    additional_args[#additional_args + 1] = "--encoding=" .. opts.file_encoding
+  end
+
   if search == "" then
     search = { "-v", "--", "^[[:space:]]*$" }
   else