chore: add script for updating local snapshots (#28254)

Issue number: N/A

---------

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issue. -->

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## What is the current behavior?
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Team members often need to update the ground truth screenshots when
validating visual regressions or working on a design change. The command
may be unfamiliar to them or they may be new to the project/playwright.

## What is the new behavior?
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this PR. -->

- Adds a new script to the `core` package for updating the local (to the
file system) ground truth screenshots.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

Author: sean-perkins

core/package.json

@@ -95,6 +95,7 @@
     "test.spec": "stencil test --spec --max-workers=2",
     "test.spec.debug": "npx --node-arg=\"--inspect-brk\" stencil test --spec",
     "test.e2e": "npx playwright test",
+    "test.e2e.update-snapshots": "npm run test.e2e -- --update-snapshots",
     "test.watch": "jest --watch --no-cache",
     "test.treeshake": "node scripts/treeshaking.js dist/index.js",
     "validate": "npm run lint && npm run test && npm run build && npm run test.treeshake"

core/src/utils/test/playwright/docs/usage-instructions.md

@@ -59,7 +59,13 @@ The examples provided in the [Running Tests](#running-tests) section also apply
 Note that since you are generating the reference branch ground truth screenshots, you must be on the reference branch locally. Don't forget to pull the latest reference branch changes and then re-build using `npm run build`.
 
 ```shell
-npm run test.e2e -- --update-snapshots
+npm run test.e2e.update-snapshots
+```
+
+Optionally, you can pass a directory to only update the ground truths for that directory & subdirectories. This is useful when working on a specific component.
+
+```shell
+npm run test.e2e.update-snapshots src/components/alert/
 ```
 
 From here, you can switch back to your branch and run the tests.