jsgen: fix maps are always constructed using string keys (fix #24607 #24671)

[gchumillas]

Fixes #24607 and #24671

The original problem is that map keys do not preserve the prototype methods of the original key values. The trick is to store the original key values, along with their prototype, so the following V code:

m := {
	1: 'one'
	2: 'two'
	3: 'three'
}

Is translated to this JS code:

const map = {
	"map": {
		// the `key` property preserves the original key value, along with its prototype
		"1": { "val": { "str": "one" }, "key": { "val": 1 } },
		"2": { "val": { "str": "two" }, "key": { "val": 2 } },
		"3": { "val": { "str": "three" }, "key": { "val": 3 } }
	},
	"length": 3
};

Later, we can then use the "key values" for other purposes, such as returning the keys from the map.

[huly-for-github]

Connected to Huly®: V_0.6-23030

[spytheman]

Please add new test functions, instead of modifying the existing ones, unless there is a bug. That makes reviewing a lot easier.

[spytheman]

Excellent work.