[table] fix issues with blank rows/columns on mount/resize

[adidahiya]

fixes #3779, #3941

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

• Update the "basic usage" table example to repro the bug described in Blank table when resizing columns #3941
• Adjust some viewport rect code to be more defensive about and provide defaults (top = 0, left = 0) for when the scroll container element ref is null, or doesn't have client coordinates. This fixes the edge cases where the visible grid would be incorrectly calculated as the top left 4x4 cells, and only those cells would render

Reviewers should focus on:

N/A

Screenshot

[adidahiya]

This is a relatively safe change and it passes the test suite, so I'm going to push it through to verify that it fixes the related bugs in practice.