std.builtin: rename Type.Fn's args to params

This was a poor naming choice; these are parameters, not arguments.
Parameters specify what kind of arguments are expected, whereas the arguments are the actual values passed.

lib/std/fmt.zig

@@ -1724,7 +1724,7 @@ pub const ParseIntError = error{
 ///     ) !void;
 ///
 pub fn Formatter(comptime format_fn: anytype) type {
-    const Data = @typeInfo(@TypeOf(format_fn)).Fn.args[0].type.?;
+    const Data = @typeInfo(@TypeOf(format_fn)).Fn.params[0].type.?;
     return struct {
         data: Data,
         pub fn format(