Rename Shape to Border and remove legacy border radius alias values

[alex-page]

WHY are these changes introduced?

Border tokens are under a category called shape which is not clear to users. All of the values are categorised as ShapeBorder so removing Shape simplifies this category. The tokens also have confusing legacy aliases which breaks the scale.

WHAT is this pull request doing?

• Remove border-radius-base
• Remove border-radius-large
• Replace border-radius-half
• Rename token group Shape to Border
• Fail linter when there is usage of border-radius-base border-radius-large and border-radius-half
• Replace shape tokens page with border on polaris.shopify.com

[github-actions]

size-limit report 📦

Path	Size
polaris-react-cjs	216.01 KB (-0.03% 🔽)
polaris-react-esm	138.91 KB (-0.02% 🔽)
polaris-react-esnext	194.09 KB (-0.03% 🔽)
polaris-react-css	41.92 KB (-0.05% 🔽)

[lgriffee]

LGTM! 🚢✨💯 Only thought would be to include an entry in documentation/guides/migrating-from-v10-to-v11.md about this change as well.

[aaronccasanova]

Suggested change

	const defaultBorderRadius = '2' as BorderRadiusScale;
	const defaultBorderRadius: BorderRadiusScale = '2';

Also, can we move this value outside the body of the function?

[aaronccasanova]

Reminder to rename the file as well

[lgriffee]

If we are removing these tokens won't they get flagged? Is this needed? Mentioning this to @aaronccasanova earlier and was just starting to chat about it. Following up on that convo here.

[alex-page]

Yes. Removing these tokens is a bit weird to add them to the linter. The reason I think we should do this is to encourage people to use the latest version and use the tokens as intended. At some point in the future this can definitely be removed.

[lgriffee]

LGTM! 🚢✨💯 Only thought would be to include an entry in documentation/guides/migrating-from-v10-to-v11.md about this change as well.

I'm working on documentation for removing tokens on another branch. If you follow this format below for the token removal portion of the documentation then it should avoid conflicts. No worries though if another way makes more sense! And I assume you'll also be creating another section talking about the token grouping rename so no worries if it breaks the format below.

## Tokens

The following tokens have either been renamed or removed. You will need to replace any instances of them with their new name or value equivalents.

| Deprecated Token          | Replacement Value        |
| ------------------------- | ------------------------ |
| `--p-border-radius-base`  | `--p-border-radius-1`    |
| `--p-border-radius-large` | `--p-border-radius-2`    |
| `--p-border-radius-half`  | `--p-border-radius-full` |