Improve _value type for single select: Allow arbitrary values

[sdvg]

Refs: #7387

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PR Overview

This pull request updates the _value property for the single select component to allow arbitrary values instead of only strings. Key changes include updating the types and validation logic in the controller, schema, and shadow files to use StencilUnknown.

Reviewed Changes

File	Description
packages/components/src/components/single-select/controller.ts	Updated the validateValue method to use StencilUnknown and watchValidator instead of watchString
packages/components/src/schema/components/single-select.ts	Changed the _value prop type from string to StencilUnknown
packages/components/src/components/single-select/shadow.tsx	Modified _value type and related methods (getValue, updateInputValue) to support StencilUnknown

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

packages/components/src/components/single-select/controller.ts:47

• Using Boolean as the validator may not be sufficient for validating arbitrary values. Consider reviewing if a more appropriate validation function or mechanism is needed to handle the wider range of types allowed by StencilUnknown.

watchValidator(this.component, '_value', Boolean, new Set([`StencilUnknown`]), value);