Revamping to matrix style

node_modules/@jridgewell/set-array/README.md

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+# @jridgewell/set-array
+
+> Like a Set, but provides the index of the `key` in the backing array
+
+This is designed to allow synchronizing a second array with the contents of the backing array, like
+how in a sourcemap `sourcesContent[i]` is the source content associated with `source[i]`, and there
+are never duplicates.
+
+## Installation
+
+```sh
+npm install @jridgewell/set-array
+```
+
+## Usage
+
+```js
+import { SetArray, get, put, pop } from '@jridgewell/set-array';
+
+const sa = new SetArray();
+
+let index = put(sa, 'first');
+assert.strictEqual(index, 0);
+
+index = put(sa, 'second');
+assert.strictEqual(index, 1);
+
+assert.deepEqual(sa.array, [ 'first', 'second' ]);
+
+index = get(sa, 'first');
+assert.strictEqual(index, 0);
+
+pop(sa);
+index = get(sa, 'second');
+assert.strictEqual(index, undefined);
+assert.deepEqual(sa.array, [ 'first' ]);
+```