Monetize: move export supporters button to fix issues with infinite scroll

[simison]

Resolves #89108

Proposed Changes

• Moves export button from footer to header, to avoid issues with infinite scrolling on longer lists.
• Change button copy to simpler "Export" to be in line with other export functionality elsewhere (content, subscribers).

I left the mobile version as-is for now:

Testing Instructions

• With paid subscribers on the site, load /earn/supporters/SITE with different screen sizes.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-102756

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-102756&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-102756&env=a8c-for-agencies

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/monetize-supporters-move-export-button on your sandbox.

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~36 bytes added 📈 [gzipped])

name  parsed_size           gzip_size
earn       +205 B  (+0.0%)      +36 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[crisbusquets]

Works for me, @simison !

I agree with what you mentioned here (#89108 (comment)):

Moved the button to the table heading in #89111 since that was the simplest approach with the current code structure.
It's also semantically at the right level since heading is shared between other pages.

[simison]

Closing as we'll need more work at the backend for better UX; the placement like this won't work since downloading full list works only once they've scrolled through the whole list.