feat(gcds-file-uploader): Add native HTML attributes and validation

[ethanWallace]

Summary | Résumé

Add attributes to match gcds-file-uploader behaviour to the HTML select to provide additional validation.

gcds-file-uploader has also been expanded to work with the HTML ValidityState to provide developers with more options when validating gcds-file-uploaders and new methods to check current validation state.

New properties/attributes

Property	Attribute	Description	Type	Default
autofocus	autofocus	If true, the file-uploader will be focused on component render	boolean	undefined
form	form	The ID of the form that the file-uploader field belongs to.	string	undefined
validity	validity	Read-only property of the select, returns a ValidityState object that represents the validity states this element is in.	ValidityState	undefined

New methods

Name	Description	Returns
checkValidity()	Check the validity of gcds-file-uploader	boolean
getValidationMessage()	Get validationMessage of gcds-file-uploader	string

cds-snc/design-gc-conception#2026