Add Field level tooltip to Combobox / Deprecate Input assistiveText.fieldLevelHelpButton

[davidlygagnon]

Fixes #1681

Additional description

• Adding fieldLevelHelpTooltip to combobox component. Inspired by fieldLevelHelpTooltip prop on input component :)

Work by @interactivellama

• Deprecate Input’s assistiveText.fieldLevelHelpButton prop and add a checkProp warning to use fieldLevelHelpTooltip's assistiveText.triggerLearnMoreIcon.
• Centralizes the default Tooltip props into it’s own module, so that code can be re-used across Combobox and Input.
• Combobox/Input: Use Tooltip's learnMore variant
• Documents triggerStyle: { position: 'static' } usage and removes overflowBoundaryElement from example
• Remove default for Input’s assistiveText.fieldLevelHelpButton so that Tooltip has the default “Help” text and not the Input component. Having defaults in two locations causing problems when merging objects, since defaults mean that default props are defined.
• Revert to use of ButtonIcon within a Button component in order to make the info icon slightly smaller due to the removal of a span tag that wraps <Button><Icon/></Button but not if Button's icon props are used.

Console warning

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[hajiz]

Hi @interactivellama , what is the latest status on this PR? Any plan to merge this in? Thanks.

Please let me know if any work is required before this PR can be submitted.

[interactivellama]

@hajiz No, it's just been the Christmas/New Year holiday delay. I took a quick glance. I think I can merge this into master tomorrow.

[interactivellama]

@hajiz It is now merged. Would you like a release next week?

[hajiz]

Hi @interactivellama , thanks for merging the PR. We would ultimately love to have a release, but please let me figure out some dependencies and will get back to you shortly.