checker: check enum fields with duplicate value (fix #19309)

[yuyi98]

This PR check enum fields with duplicate value (fix #19309).

• Check enum fields with duplicate value.
• Add test.

pub enum HardwareAccelerationDevice as i64 {
	@none = 0
	cpu = (1 << 0)
	gpu = (1 << 1)
	accelerator = (1 << 2)
	default = (1 << 0)
	all = 0xFFFFFFFF
}

fn main() {
	device := HardwareAccelerationDevice.@none
	println(device)
}

PS D:\Test\v\tt1> v run .    
tt1.v:6:12: error: enum value `1` already exists
    4 |     gpu = (1 << 1)
    5 |     accelerator = (1 << 2)
    6 |     default = (1 << 0)
      |               ~~~~~~~~
    7 |     all = 0xFFFFFFFF
    8 | }

[spytheman]

The new code is very repetitive, and it does not handle the overflow cases (see the ast.IntegerLiteral branch from above). Imho extract a common method, that takes the expression and the low/high values, and call it in all branches.

[yuyi98]

OK， I see.

[spytheman]

Excellent work.