fix(bigquery): ensure that count distinct can be used in window functions without a specified window

[cpcloud]

Allow bigquery count distinct in window functions if window is the whole table. Closes #10390.

[cpcloud]

BigQuery passing after this change:

cloud in 🌐 falcon in …/ibis on  fix-bigquery-count-distinct-windows is 📦 v10.1.0 via 🐍 v3.12.9 via ❄️  impure (ibis-3.12-env) took 20s
❯ pytest -m bigquery -n auto --dist loadgroup --snapshot-update -q
bringing up nodes...
..sssssssssssssssssssss....x.....xxx....x......x.......x...........x...........x.x..........x......................................................x............x......x........x.......................x...x.x..xxx.............xxxxxxxxxxxxx.xx.xxxx.xxx.xxsssssssssssssssssssssssssssssssssssssssssxsss.sssssssssssssssssssssssssssssssssssssss.xsxsssssssssssssssx.x.xxxxxxxxxxxxxxxx. [ 16%]
xx.x.xxxxxxxxxxxxxxxxxx.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxxxxxxxxxxxxx...x..x.....x.xxxx.x.x....x....x.........x...........x....x.x.x.xx.xx.xxx...x....xx..x..x....x...........x.........x...........x..xx........x..x.xxx...xxxx.xx...x.......x....xx..x......x........xx..............x..x.xx.x.........x..x....x.....x...x.xxx.x.......x............x...x....x.x............xx..... [ 33%]
...........x..........................x......x.xx.......x...xx..x..xxx.....xx.xxxx.xxx...x....x...x....x.x.x..x....xx.........x.....xxx........x..x...x.x..............x.........x....xx.....x..x...x.......x..........X.x.Xx......x...............XXx........................x..........x................x.x............................................................................. [ 49%]
.x.x.......x..........x.......x.......x..........................s........x...xx....xx..xx..x.xx.xxxx.x.x...x.xx....xx....x....x.....x..x.x...x.xx.........x......xx..xx................s......x........s....sx..s.................x.....x...x.....x............x.............x.x.x.....x.x.....x...........x.x.................x....x.xx................x......x..x...................... [ 66%]
.....................x.x....x....x......x....x.....x............x.............xx.....x..............................s..........s...............s.....................................x.......x........x......xxxxxxxxxxx................................x...........x....x.....................................s.............s....s.........s............................................. [ 82%]
.........x.......xx.................................................................................................................................................x..................................................................................................................................................................................................................... [ 99%]
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1785 passed, 132 skipped, 358 xfailed, 4 xpassed in 306.31s (0:05:06)