fix(core,table): forward ref types

[redallen]

What: Closes #3824 again:

• Upgrade typescript from 3.4.5 to ^3.8.3 for proper Omit support.
• Change our forwarded ref components DataToolbarGroup, TabButton, TabContent, and TextInput to all use the same interface:

export const TabContent = React.forwardRef((props: TabContentProps, ref: React.Ref<HTMLElement>) => (
  <TabContentBase {...props} innerRef={ref} />
));

which produce pretty types for consumers:

export declare const TabContent: React.ForwardRefExoticComponent<TabContentProps & React.RefAttributes<HTMLElement>>;

• Remove single remaining use of typescript helper OneOf left over from prop-types conversion
• Fix incorrect react-icons proptype for size

[patternfly-build]

PF4 preview: https://patternfly-react-pr-3919.surge.sh
A11y report: https://patternfly-react-pr-3919-coverage.surge.sh

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@b696cec). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #3919   +/-   ##
=========================================
  Coverage          ?   60.05%           
=========================================
  Files             ?      415           
  Lines             ?     6367           
  Branches          ?     2389           
=========================================
  Hits              ?     3824           
  Misses            ?     2093           
  Partials          ?      450

Flag	Coverage Δ
#patternfly4	60.05% <100%> (?)

Impacted Files	Coverage Δ
...eact-core/src/components/SimpleList/SimpleList.tsx	94.73% <ø> (ø)
...on/src/components/VerticalTabs/VerticalTabsTab.tsx	88.23% <ø> (ø)
...ore/src/components/OptionsMenu/OptionsMenuItem.tsx	66.66% <ø> (ø)
...eact-core/src/components/Popover/PopoverHeader.tsx	100% <ø> (ø)
...ore/src/components/ClipboardCopy/ClipboardCopy.tsx	34.14% <ø> (ø)
...-core/src/components/EmptyState/EmptyStateIcon.tsx	85.71% <ø> (ø)
...-charts/src/components/ChartLegend/ChartLegend.tsx	81.81% <ø> (ø)
packages/react-core/src/components/Nav/Nav.tsx	60.71% <ø> (ø)
...core/src/components/Progress/ProgressContainer.tsx	66.66% <ø> (ø)
...src/components/BackgroundImage/BackgroundImage.tsx	100% <ø> (ø)
... and 41 more

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[ddonahue007]

LGTM

[boaz0]

lgtm 👍