feat(select): expose container and label as CSS parts (#27541)

Issue number: resolves #27112

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## What is the current behavior?
The select does not expose the label or the container for the
value/placeholder as a CSS shadow part in order to style it.

## What is the new behavior?
- Exposed `label` and `container` parts for custom styling
- Added an e2e test to verify the parts are working
- Renamed the existing screenshots for the custom tests to fix a typo
from "custon" to "custom"

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->

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Co-authored-by: ionitron <hi@ionicframework.com>