Make initial loading indication more prominent for table pages

[pavish]

Problem

• When the table page loads, there's an empty view which gives an impression that there's something wrong with the app.
• The loading indication is at the bottom right and it's not prominent to the user.

https://github.com/mathesar-foundation/mathesar/assets/11850603/bbf6d977-10b1-4436-81fb-93cc44e6a1cb

Proposed solution

• Present a more prominent loading indication in the center of the page.

[seancolsen]

Thanks for reporting this, @pavish.

• I'm removing needs: product approval because I don't imagine that anyone would object to adding a loading indicator.

• I'm removing needs: ux design because I think this is something that we can fairly easily improvise.

• Regarding design, I suggest that we add a large loading spinner that appears within the table area, near the top, and horizontally centered.

  As precedent, here are some similar loading spinners that we have:

  • Within the record selector:

    

  • Within the import preview

    

  • On the record page:

    

  Notice that we have some inconsistency in the size and color of these loading spinners. It might be nice to fix that by adding a LargeSpinner component that we use in cases like this. But I would consider that a very low priority — something that doesn't necessarily need to be done along with adding a loading spinner to the table page.

• To me everything here seems straightforward, and this issue seems worth of moving forward, so I'm marking it as ready.

• Because I think this would be fairly easy, I'm also marking it as help wanted.