fix(lib): reorder Array#reduce/reduceRight overloads so generic <U> variant is tried first (#7014)

[creazyfrog]

Fixes #7014

Problem

TypeScript resolves overloads by picking the first matching one. In src/lib/es5.d.ts, the reduce(callbackfn, initialValue: T): T overload was listed before the reduce<U>(callbackfn, initialValue: U): U overload. This caused TypeScript to infer T[] (the less-specific type) instead of a user-provided U type in cases like:

const result = [1, 2, 3].reduce((acc, x) => { acc.push(x); return acc; }, []);
//    ^^^^^^ was: number[][]  should be: number[]

Fix

Move the generic <U> overload above the T-with-initialValue overload for all four affected groups:

• ReadonlyArray.reduce
• ReadonlyArray.reduceRight
• Array.reduce
• Array.reduceRight

No new overloads added, no signatures changed — only the declaration order.

Verification

const nums = [1, 2, 3];
const result = nums.reduce<string[]>((acc, x) => [...acc, String(x)], []);
// result: string[]  ✓