Merge OUFR and react-next into react

[ecraig12345]

This is part 1/4 in a series of changes that will happen in master after v7 development moves to a branch, but before beta publishing:

1. (this) Merge OUFR and react-next into react #15152 OUFR/react-next merge
2. Re-export date-time components from react #14679 Move date-time components
3. Move @uifabric packages under @fluentui scope #13384 uifabric/fluentui package renames
4. Set up beta releases #14689 set up beta releases

This will be done across multiple PRs, and some of the work can be split up between multiple people.

• Merge OUFR into react (1 person)
• Merge react-next into react (last chance to review FC changes). This can be split into groups of components to be done by different people. (EDIT: This was WAY more complicated than expected--see comment below.)
• Delete OUFR and update code references to react-next
• Either delete react-next or make it into a pure re-export package from react (and bump version to 9-alpha)
• Update gitignore so that removed files don't come back in a bad merge
• Update code references to react-next
• Delete "next" versions of vr/perf tests

[ecraig12345]

The "merge react-next into react" step ended up being WAY more complicated than expected. Here's the procedure and tracking we used (leaving it here for reference for future releases)...

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If the v7 component implementation is in react-internal (most components), the react-next implementation should be moved to react-internal (NOT react). In the steps, react(-internal) means whichever of the two packages is appropriate for your component.

Full steps:

1. Move the component code and tests from react-next to react(-internal). Steps:
   1. Find where the v7 component is currently located (either react-internal or react) and delete the whole folder react(-internal)/src/components/ComponentName.
   2. Move the whole folder react-next/src/components/ComponentName to react(-internal)
   3. Update any react-next or react imports in the moved code to relative imports. If it's in react-internal also change those to relative imports. (A few things must still be deep-imported from react-internal; we'll fix this later.)
2. Update the component's root file in react-next (e.g. react-next/src/Fabric.ts) to re-export from @fluentui/react/lib/ComponentName
3. Delete any *Next perf-tests or vr-tests for the component
4. Delete react-examples/src/react-next/ComponentName/docs (they should be exact duplicates; even if they're not, the react versions are more likely to be correct)
5. Compare the examples and .doc.tsx in react-examples/src/react-next/ComponentName with the react versions. If the example names and content appear unchanged you can just delete the react-next versions. Otherwise copy over the moved examples to the react folder (fixing imports to be from react), and delete any remaining react-next example/doc files.
   • Note: Even if the component is in react-internal, the examples should be under react-examples/src/react and import from @fluentui/react
6. Update snapshots and API in react(-internal) and react-next

In the PR, be sure to look at:

• Perf test: is the new implementation slower?
• Screener: any visual regressions?
• Bundle size (not sure if it will be accurate until all components move)

Component	Assignee	PR/notes
Callout	Jon	done
ChoiceGroup	Elizabeth	done
Coachmark	Elizabeth	done
ComboBox + Autofill	Jon	done
ContextualMenu	Jon	done
Dropdown	Jon	done
Fabric	Tomi	done
FloatingPicker/ExtendedPicker	Jon	done
FocusTrapZone	Mak	done
Image	Tomi	done
Layer	Caleb	done
MessageBar	Caleb	done
OverflowSet	Caleb	done
Persona	Jon	done
Popup	Mak	done
Rating	Elizabeth	done
ResizeGroup	Elizabeth	done
SearchBox	Caleb	done
SelectedItemsList	Caleb	done
Shimmer	Caleb	done
SpinButton	Caleb	done
SwatchColorPicker	Caleb	done
TextField	Elizabeth	done

Ignore/delete react-next versions due to not yet converted:

• Breadcrumb (done)
• Modal (done)
• Keytip