fix: preserve globstar in non-final extglob alternatives

[DucMinhNe]

Fixes #154.

Problem

In a negation extglob like !(a/**|b/**), the result depends on the order of the alternatives:

const pm = require('picomatch');
const opts = { dot: true };

pm('!(a/**|b/**)**', opts)('a/x/y'); // => true  (wrong — a/** should exclude it)
pm('!(b/**|a/**)**', opts)('a/x/y'); // => false (correct)

Only the last alternative's ** compiles to a real globstar. Every non-final alternative's ** is silently downgraded to a single path segment ([^/]*?), so it can't match deep paths inside the lookahead — and the negation fails to exclude them.

Cause

The globstar-downgrade guard in push (lib/parse.js) keeps a ** as a globstar when the following token is a pipe:

const isExtglob = tok.extglob === true || (extglobs.length && (tok.type === 'pipe' || tok.type === 'paren'));

But the | token is pushed as { type: 'text', value: '|' } (see the Pipes branch), never type: 'pipe'. So tok.type === 'pipe' is effectively dead code and the preceding globstar gets downgraded. The last alternative survives only because it is followed by ) (type: 'paren', which is guarded) — hence the order-dependence.

Fix

Also treat a token whose value is | as an extglob boundary:

const isExtglob = tok.extglob === true || (extglobs.length && (tok.type === 'pipe' || tok.value === '|' || tok.type === 'paren'));

This is surgical — it only affects ** immediately followed by | inside an extglob.

Tests

Added a regression test in test/extglobs.js asserting the negation result is independent of alternative order, that the last alternative still excludes deep paths, and that unrelated paths are still matched (no over-exclusion).

Full suite: 1976 passing, lint clean. Verified the new test fails on master and passes with the fix.