TS Fix: allow string | number on StoreFilterField.width prop

[cnrudd]

TS Fix: allow "string | number", not just "number" on StoreFilterField "width" prop, since underlying TextInput in desktop and mobile takes "string | number" for "width". A string width like '100%' can be useful when the StoreFilterField is the only field in a narrow "picker" grid's toolbar, and you want the field's width to adjust with the user's adjustment of the grid panel width, so that the field's clear button always stays visible.

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• Caught up with develop branch as of last change.
• Added CHANGELOG entry:not required, just a TS fix
• Reviewed for breaking changes: not a breaking change
• Updated doc comments / prop-types: docs updated
• Reviewed and tested on Mobile: reviewed, testing not required.
• Created Toolbox branch: not required.

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