fix(tooltip): correct positioning when unstyled is applied

[williaster]

🐛 Bug Fix

This PR

• fixes TooltipWithBounds bug #767 where setting unstyled on TooltipWithBounds breaks positioning because it is passed to Tooltip, which then doesn't respect the style prop which includes the needed offset
• fixes an issue where if unstyled is set on either Tooltip or TooltipWithBounds, lib consumers must also minimally set .visx-tooltip { position: absolute; } themselves in order for the tooltips to be correctly positioned since they rely on absolute positioning.
  • this was fixed by removing position: absolute from defaultStyles, and always setting it (along with the positional offset)

Testing
Verified in /tooltip demo that tooltip is correctly positioned when unstyled is set for all combinations

• boundary detection + portal
• boundary detection + portal
• boundary detection + portal
• boundary detection + portal

@hshoff @kristw @singhanurag05

[coveralls]

Pull Request Test Coverage Report for Build 282956020

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.08%) to 54.417%

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Totals
Change from base Build 42:	0.08%
Covered Lines:	1099
Relevant Lines:	1976

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💛 - Coveralls

[torkelo]

Nice! just ran into this today!

[williaster]

Closing in favor of #828