feat(select): add parts support for placeholder, icon, text

[liamdebeasi]

#20916

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Discussed with the team and we decided we did not want to expose this right now.

What is the new behavior?

• Removed icon-inner part

Does this introduce a breaking change?

• Yes
• No

Other information

[brandyscarney]

Can we also use this to uncomment the docs for part?

[liamdebeasi]

@brandyscarney Yeah docs support for it is now in Stencil, so I can remove the "TODO" in all the PRs

[brandyscarney]

When we merge this let's do it as a feature to add the parts since it's going in the public API

feat(select): add parts support for placeholder, icon, text

[brandyscarney]

Or break it up into two, whichever you want