LibJS: Allow "approximately" results to differ in plural form

This is a normative change in the Intl.NumberFormat V3 spec. See:
08f599b

Note that this didn't seem to actually affect our implementation. The
Unicode spec states:

https://www.unicode.org/reports/tr35/tr35-53/tr35-numbers.html#Plural_Ranges
"If there is no value for a <start,end> pair, the default result is end"

Therefore, our implementation did not have the behavior noted by the
issue this normative change addressed:

    const pr = new Intl.PluralRules("en-US");
    pr.selectRange(1, 1); // Is "other", should be "one"

Our implementation already returned "one" here because there is no such
<start=one, end=one> value in the CLDR for en-US. Thus, we already
returned the end value of "one".

Userland/Libraries/LibJS/Tests/builtins/Intl/PluralRules/PluralRules.prototype.selectRange.js

@@ -39,11 +39,13 @@ describe("errors", () => {
 describe("correct behavior", () => {
     test("basic functionality", () => {
         const en = new Intl.PluralRules("en");
+        expect(en.selectRange(1, 1)).toBe("one"); // one + one = one
         expect(en.selectRange(1, 2)).toBe("other"); // one + other = other
         expect(en.selectRange(0, 1)).toBe("other"); // other + one = other
         expect(en.selectRange(2, 3)).toBe("other"); // other + other = other
 
         const pl = new Intl.PluralRules("pl");
+        expect(pl.selectRange(1, 1)).toBe("one"); // one + one = one
         expect(pl.selectRange(1, 2)).toBe("few"); // one + few = few
         expect(pl.selectRange(1, 5)).toBe("many"); // one + many = many
         expect(pl.selectRange(1, 3.14)).toBe("other"); // one + other = other