fix(id): escape values assigned through the value setter

[greymoth-jp]

ID doesn't override value, so assigning to id.value stores the string as-is and toString() emits it unescaped. ClassName has had an escaping value setter since d4dda8c5 ("Escape class name values by default", 2018), but ID never got the same one, even though class and id selectors are both identifiers and follow the same escaping rules.

The result is wrong output for any id value that contains characters needing escapes:

const parser = require("postcss-selector-parser");

const cls = parser.className({ value: "x" });
cls.value = "foo.bar";
cls.toString(); // ".foo\\.bar"   (correct)

const id = parser.id({ value: "x" });
id.value = "foo.bar";
id.toString(); // "#foo.bar"   (wrong: re-parses to id "foo" + class "bar")

Leading digits, spaces and # break the same way: #1abc, #a b, #a#b.

This adds the same setter ClassName uses (cssesc(v, { isIdentifier: true }) stored into raws.value), so id values escape on assignment:

id.value = "foo.bar";
id.toString(); // "#foo\\.bar"

The new test mirrors the existing ClassName#set value test. npm test passes (lint, typecheck, full suite).