checker: fix checking give const map as default or init value to struct fields(fix #20512)

[shove70]

1. Fixed Mutable map field, initialised with const, makes const mutable #20512
2. Add tests.

const const_map = {
	'key': 4
}

struct Foo {
mut:
	field map[string]int = const_map
}

fn main() {
	_ = Foo{
		field: const_map
	}
}

outputs:

a.v:7:25: error: cannot copy map: call `move` or `clone` method (or use a reference)
    5 | struct Foo {
    6 | mut:
    7 |     field map[string]int = const_map
      |                            ~~~~~~~~~
    8 | }
    9 |
a.v:12:10: error: cannot assign a const map to mut struct field, call `clone` method (or use a reference)
   10 | fn main() {
   11 |     _ = Foo{
   12 |         field: const_map
      |                ~~~~~~~~~
   13 |     }
   14 | }