parser, checker: check $veb.html('index.html') (fix #21929)

[yuyi98]

This PR check $veb.html('index.html') (fix #21929).

• Check $veb.html('index.html').
• Add test.

import veb
import vweb

fn main() {
	$veb.html('index.html')
	$vweb.html('index.html')
}

PS D:\Test\v\tt1> v run .
tt1.v:5:2: error: `$veb.html()` must be called inside a web method, e.g. `fn (mut app App) foo(mut ctx Context) veb.Result { return $veb.html('index.html') }`
    3 | 
    4 | fn main() {
    5 |     $veb.html('index.html')
      |     ~~~~~~~~~~~~~~~~~~~~~~~
    6 |     $vweb.html('index.html')
    7 | }
tt1.v:6:2: error: `$vweb.html()` must be called inside a web method, e.g. `fn (mut app App) foo(mut ctx Context) vweb.Result { return $vweb.html('index.html') }`
    4 | fn main() {
    5 |     $veb.html('index.html')
    6 |     $vweb.html('index.html')
      |     ~~~~~~~~~~~~~~~~~~~~~~~~
    7 | }

[spytheman]

Excellent work.