Add zero tokens for consistency as per team decision

Author: jesstelford

.changeset/brown-ghosts-cough.md

@@ -0,0 +1,5 @@
+---
+'@shopify/polaris-tokens': minor
+---
+
+Add 0 tokens where missing as per [the team's decision](https://github.com/Shopify/polaris/discussions/7334#discussioncomment-4988991).

polaris-tokens/src/themes/base/border.ts

@@ -16,7 +16,7 @@ export type BorderRadiusAlias = 'full';
 
 export type BorderRadiusAliasOrScale = BorderRadiusAlias | BorderRadiusScale;
 
-export type BorderWidthScale = '0165' | '025' | '050' | '100';
+export type BorderWidthScale = '0' | '0165' | '025' | '050' | '100';
 
 export type BorderTokenName =
   | `border-radius-${BorderRadiusAliasOrScale}`
@@ -59,6 +59,9 @@ export const border: {
   'border-radius-full': {
     value: '9999px',
   },
+  'border-width-0': {
+    value: size['0'],
+  },
   'border-width-0165': {
     value: size['0165'],
   },

polaris-tokens/src/themes/base/zIndex.ts

@@ -1,6 +1,7 @@
 import type {MetaTokenProperties} from '../types';
 
 export type ZIndexZScale =
+  | '0'
   | '1'
   | '2'
   | '3'
@@ -23,6 +24,9 @@ export type ZIndexTokenGroup = {
 export const zIndex: {
   [TokenName in ZIndexTokenName]: MetaTokenProperties;
 } = {
+  'z-index-0': {
+    value: 'auto',
+  },
   'z-index-1': {
     value: '100',
   },