[SR-11461] Improve next(upperBound) to use all bits generated

[stephentyrone]

Previous ID	SR-11461
Radar	None
Original Reporter	@stephentyrone
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Bug, numerics
Assignee	None
Priority	Medium

md5: 1bf7de03366049df3706fdb318f05510

Issue Description:

For small integer types,

[stephentyrone]

CC @Azoy @natecook1000

[Azoy]

Could we do number 1 for the short term and look at going for number 2 in the long term? Am I correct in thinking that buffering draws would be something along the lines of a `fillBytes` method? Would both approaches require an evolution proposal? The first option seems like it could be added at anytime (while alerting people on the forums ofc).

[stephentyrone]

The first definitely does not require evolution. The second would. And yes, the first can be done quickly (I was planning to do it while traveling this weekend).