feat: Add stable id.setBaseId method

[diegohaz]

This PR marks the id.unstable_setBaseId method as stable.

Does this PR introduce a breaking change?

No. But people relying on the unstable feature will have to update their code.

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[github-actions]

Size Change: -4 B (0%)

Total Size: 251 kB

Filename	Size	Change
packages/reakit/dist/reakit.min.js	31.7 kB	-4 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
packages/reakit-playground/dist/reakit-playground.min.js	186 kB	0 B
packages/reakit-system-bootstrap/dist/reakit-system-bootstrap.min.js	19.2 kB	0 B
packages/reakit-system-palette/dist/reakit-system-palette.min.js	8.84 kB	0 B
packages/reakit-system/dist/reakit-system.min.js	2.21 kB	0 B
packages/reakit-utils/dist/reakit-utils.min.js	3.11 kB	0 B

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[codecov]

Codecov Report

Merging #691 into next will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             next     #691   +/-   ##
=======================================
  Coverage   95.49%   95.49%           
=======================================
  Files         176      176           
  Lines        2821     2821           
  Branches      722      722           
=======================================
  Hits         2694     2694           
  Misses        127      127           

Impacted Files	Coverage Δ
packages/reakit/src/Composite/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Dialog/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Disclosure/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Form/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Grid/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Id/IdState.ts	100.00% <ø> (ø)
packages/reakit/src/Menu/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Popover/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Radio/__keys.ts	100.00% <ø> (ø)
packages/reakit/src/Rover/__keys.ts	100.00% <ø> (ø)
... and 4 more

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