ADR 010: Merge drafts status into experimental

contributor-docs/adrs/adr-010-drafts-are-experimental.md

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+# ADR 010: Merge drafts status into experimental
+
+## Status
+
+Draft
+
+## Context
+
+`Drafts` were introduced in [ADR-006](./adrs/adr-006-drafts.md) as a way of creating components outside of the root bundle of `@primer/react`. This helps us create, test and maintain multiple versions of the same component in parallel.
+
+Example:
+
+```js
+// default version of component exported from root of package
+import {UnderlineNav} from '@primer/react'
+
+// new version of component exported from /drafts
+import {UnderlineNav} from '@primer/react/drafts'
+```
+
+We have also used this method for components that are still a work in progress and we don't want developers to start using them in production without collaborating with us first.
+
+Example:
+
+```js
+// this component only exists in drafts and not in the roof of the package
+import {TreeView} from '@primer/react/drafts'
+```
+
+### Why do we not reuse `experimental` status?
+
+The reason we do not use `experimental` label for these components is because `drafts` conveys a different message than maturity on the [component lifecycle](https://primer.style/contribute/component-lifecycle).
+
+A `draft` component can be further along on the component lifecycle than `experimental`, but still not be the recommended version of the component until the next major release (to plan breaking changes better). For example, at the time of writing, the [new UnderlineNav2 in drafts](https://primer.style/react/drafts/UnderlineNav2) has been reviewed for accessibility and is almost at `Beta` maturity. We can call it a `draft` component with `beta` maturity.
+
+### Problem
+
+This is very confusing. While the above separation is useful for maintainers of primer, it is less useful to consumers.
+
+1. Consumers of primer are often confused to not find `draft` maturity on the component lifecycle.
+2. It is similar to `experimental` label in the most important characteristic to consumers - The component is not ready for production usage.
+
+### Decision
+
+We should drop the `draft` label and use `experimental` instead.
+
+While not completely accurate (UnderlineNav2 is much more polished than `experimental` maturity), the lack of confusion makes it a good trade-off.
+
+Fine-grained information about component maturity, useful for maintainers, is also communicated by the [status checklist in the component documentation](https://primer.style/react/drafts/UnderlineNav2#status).
+
+### Side effects
+
+We should create a new parallel import path for `@primer/react/experimental`.
+
+```diff
+// new version of component exported from /experimental
+- import { UnderlineNav } from '@primer/react/drafts'
++ import { UnderlineNav } from '@primer/react/experimental'
+```
+
+We would need to keep `@primer/react/drafts` in the short term as well for backwards compatibility.