[code_builder] `external` and `static` in wrong order for fields

[nikeokoronkwo]

Description

I was trying to create a field on an extension type making use of external and static (representing static properties on JS objects, for this particular use case):

return Field((f) => f
  ..external = true
  ..static = true
  // more
);

Expected Behavior

I expected that the rendered code would produce something similar to the following

external static JSEnum Blue = /* value */;

This is similar to expected behaviour described in the example here

Actual Behaviour

The code produced was instead the following

static external JSEnum Blue = /* value */;

This code does not work, as passing this through the DartFormatter in dart_style produced the following error (separate example):

line 41, column 8 of .: The modifier 'external' should be before the modifier 'static'.
   ╷
41 │ static external final MathConstants Random;
   │        ^^^^^^^^
   ╵
line 43, column 8 of .: The modifier 'external' should be before the modifier 'static'.
   ╷
43 │ static external final MathConstants Length;
   │        ^^^^^^^^

Reason

After some digging, I found that this was coming from the following:

tools/pkgs/code_builder/lib/src/emitter.dart

Lines 440 to 448 in 7bf22c9

	if (spec.static) {
	output.write('static ');
	}
	if (spec.late && _useNullSafetySyntax) {
	output.write('late ');
	}
	if (spec.external) {
	output.write('external ');
	}

[nikeokoronkwo]

I would be willing to help out with this, if possible.

[devoncarew]

I would be willing to help out with this, if possible.

Sounds great! We'll just want to be careful to not regress any other keyword order considerations. It sounds like we want external static; I know that - of those three keywords - we also want static late.

[nikeokoronkwo]

#2120