Switch grid display mode to fix scrolling

[JamesNK]

Description

This is a proper fix for the scrolling issues in grids:

• Enables table mode on virtualized grids
• Refactor widths to be set on columns instead of GridTemplateColumns
• Update widths to be set as percentages instead of fractions on columns
• Reduce overscan count to improve performance

There are some issues with this change that I believe are issues in FluentUI:

• Empty and loading templates column span is broken
• Pixel width columns aren't sized correctly on refresh
• Column resizing in general doesn't feel good. Some columns can't be decreased, some columns immediately increase in size on resize

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No