Respect showOutsideDays prop for single month date range

[evansjohnson]

Fixes https://github.com/palantir/blueprint/issues/4373

Checklist

• [x] Includes tests
• [x] Update documentation

Changes proposed in this pull request:

When a DateRangePicker3 is limited to a single month, respect the showOutsideDays passed on dayPickerProps. Per https://github.com/palantir/blueprint/pull/586/files#r98813760 it was explicitly decided that showing outside days when multiple months are shown is not intended, and I agree that it still leads to some weird questions, but for a single month these issues do not exist.

Reviewers should focus on:

• Is this the behavior we want?
• Do the updated docs look good?
• Only fixing on DateRangePicker3 since DateRangePicker is deprecated and frozen.

Alternate option

Simply document that showOutsideDays is never respected for DateRangePicker3

Screenshot

[svc-palantir-github]

assert warn

Build artifact links for this commit: documentation | landing | table | demo

This is an automated comment from the deploy-preview CircleCI job.