[terra-select] Update placeholders and allowClear

[neilpfeiffer]

Feature Request

Description

As part of removing placeholders in form inputs for better accessibility, the Form Select inputs will also have a higher level of Cerner UX Design Standard requirements to provide a common and consistent placeholder pattern that is no longer editable by consumers.

Similar to Native Select, allowClear now becomes a default feature included with SingleSelect, and isFilterStyle is added for cases where a value must always be selected and not cleared, commonly found in filters and toolbars.

Related to

[terra-form-input] Insufficient color-contrast for placeholder #2992

[neilpfeiffer]

The alteration direction below is copied from #2992 (comment)

---

Alteration directions for:

• terra-form-select
• terra-form-select/lib/SelectField
• terra-form-select/lib/SingleSelect
• terra-form-select/lib/SingleSelectField
• terra-form-select/lib/Combobox
• terra-form-select/lib/ComboboxField
• terra-form-select/lib/MultiSelect
• terra-form-select/lib/MultiSelectField
• terra-form-select/lib/TagSelect
• terra-form-select/lib/TagSelectField
• terra-form-select/lib/SearchSelect
• terra-form-select/lib/SearchSelectField

---

• All forms of select: remove the placeholder prop that allows consumers to customize the placeholder text
• All forms of select: the default text given to the component as the placeholder is - Select -
• For SingleSelect, remove the allowClear prop, making the functionality the default behavior.
• For SingleSelect, add a new prop isFilterStyle to match native-select that removes the ability to have no value selected, showing a placeholder, and ability to clear an already selected value.
• Theming changes:
  Default theme:
  placeholder color: rgba(21, 33, 41, 0.62)
  placeholder font-style: italic
  disabled placeholder color:rgba(21, 33, 41, 0.62)
  Fusion theme:
  placeholder color: #707070
  placeholder font-style: normal
  disabled placeholder color: #c4c6c7
  Lowlight theme:
  placeholder color: #6f7477
  placeholder font-style: italic
  disabled placeholder color: #6f7477
• Add major version Upgrade Guide that includes these comments:
  TODO add the language needed for the accessibility and human factors guidance switching from consumers providing placeholders to providing more detailed help text with Field compositions.

[stale]

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