fix: add save button to export sets modal

[cuserox]

Why does this PR exist?

Previously, selecting sets to export would always persist the changes. This gives the user to option to save or cancel.

Closes #2575 (N.B. screen doesn't contain a search any more)

What does this pull request do?

• Renders a footer on set selection with cancel (destroys the set selection) or confirm (persists the set selection)
• Adds a previousSelectedSets state to remember the T-1 state and use when the user presses cancel (in the footer) or the back arrow (in the header)

Testing this change

• Click on 'Styles & Variables' ---> 'Export styles & variables'
• On the modal, click 'Confirm'
• Click on the 'Token Sets' tab
• Click on 'Change Sets' CTA
• Change set selections as you wish:
  • Clicking on confirm will save the changes
  • Clicking on cancel will discard the changes

Before / After

Changes in action

https://github.com/tokens-studio/figma-plugin/assets/114073780/3c0f5d9b-98f9-4c84-8a7e-d35c0276fba1

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 6129988d3bbe2d6291a3397cea9fc62ecca435d5

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[cuserox]

@LukeFinch 🎨 Footer was a copy-pasta from another area of the plugin. Can tweak if needed!

[LukeFinch]

@LukeFinch 🎨 Footer was a copy-pasta from another area of the plugin. Can tweak if needed!

Looks geeat!