chore(angular,react,vue): copy css with build.watch (#28934)

Issue number: N/A

---------

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## What is the current behavior?
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CSS is not copied from the `core/` package when running each respective
framework package in watch mode.

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

- Copies the global styles from the `core/` package to each respective
framework package when running the build in watch mode.

Note: This does not register a file watcher to copy CSS updates after
the initial command is ran. This just avoids a scenario of the global
styles being updated and the developer _not_ running a `pnpm build`
prior to running `pnpm build.watch` and the global styles not being
reflected in the framework package.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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

packages/vue/scripts/copy-css.js

@@ -1,6 +1,12 @@
 const fs = require('fs-extra');
 const path = require('path');
 
+/**
+ * Copy the CSS from the core package to the vue package.
+ * 
+ * This allows developers to import the global stylesheets
+ * from the @ionic/vue package instead of @ionic/core. 
+ */
 function copyCSS() {
   const src = path.join(__dirname, '..', '..', '..', 'core', 'css');
   const dst = path.join(__dirname, '..', 'css');