refactor(chart-controls): improve typing and file organization

[ktmud]

🏆 Enhancements
🏠 Internal

Improve typing and file organization for shared controls.

1. Reuse Metric definition in superset-ui/core.
2. Move the React components for shared controls to its own folder (prepare for adding more custom controls).
3. Export empty objects in pure typing files to fix build errors with npm link:
   

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[codecov]

Codecov Report

Merging #962 (f5bafd5) into master (d433339) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #962   +/-   ##
=======================================
  Coverage   27.70%   27.70%           
=======================================
  Files         401      401           
  Lines        8255     8255           
  Branches     1143     1143           
=======================================
  Hits         2287     2287           
  Misses       5831     5831           
  Partials      137      137           

Impacted Files	Coverage Δ
...controls/src/components/InfoTooltipWithTrigger.tsx	100.00% <ø> (ø)
...-ui-chart-controls/src/components/MetricOption.tsx	53.33% <ø> (ø)
...erset-ui-chart-controls/src/components/Tooltip.tsx	20.00% <ø> (ø)
packages/superset-ui-chart-controls/src/index.ts	100.00% <ø> (ø)
.../shared-controls/components/RadioButtonControl.tsx	9.09% <ø> (ø)
.../superset-ui-core/src/query/types/QueryFormData.ts	100.00% <ø> (ø)
...s/legacy-plugin-chart-time-table/src/TimeTable.tsx	0.00% <0.00%> (ø)

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[ktmud]

This hack fixes script errors in dev build when re-exporting pure type files:

Not sure what is the root cause, but this fixes it.

[espressoroaster]

From an offline conversation with Jesse, export default {}; is a hack solution for re-exporting * from pure type files that don't contain real JavaScript variables.

Jesse explained that there is a failure under certain circumstances that Webpack rebuild will fail and throw an error that files do not exist without the hack.

PR LGTM