Part of #18610.
Our intent is to move `definePlugin`, `defineRule`, and `eslintCompatPlugin` to a separate package `@oxlint/plugins` (plural to avoid confusion with naming convention for plugins `oxlint-plugin-xxx`).
So rename the current entry point which exports these functions from `oxlint/plugin` to `oxlint/plugins` (plural).
As we prepare for alpha release of JS plugins, it feels like we can remove the warning logged to stderr.
```
WARNING: JS plugins are experimental and not subject to semver.
Breaking changes are possible while JS plugins support is under development.
```
They do still remain experimental, but I don't think we need to shout that quite as loudly now.
## The problem
### 1. Bug with plugins outside of workspace directory
There was a bug in workspaces implementation. `loadPlugin` was assuming that the plugin file is within the workspace, but that's not necessarily the case. e.g.:
* Workspace 1: `/path/to/project/packages/foo`
* Workspace 2: `/path/to/project/packages/bar`
* JS plugin: `/path/to/project/node_modules/eslint-plugin-whatever`
This problem arises because `loadPlugin` is determining which workspace to load a plugin for by search for the workspace whose root directory contains the plugin file.
### 2. Performance
Every call to `loadPlugin`, `setupRuleConfigs`, or `lintFile` was first searching through all workspaces to find the right one (`getResponsibleWorkspace`).
This is really expensive when there are lots of workspaces, and quite expensive even when there's only 1 because iterating hashsets is relatively slow.
## This PR
This PR separates out CWD and workspace identifiers into 2 different concerns.
* Each workspace has an ID which is unique.
* Each workspace has a CWD (path to root directory as a file path).
The workspace ID is currently the workspace's root directory as a `file://...` URL. Using that as it's guaranteed unique, even for paths which are not valid UTF-8 (`Path::to_string_lossy` can produce the same `&str` for different paths). But ID it doesn't have to be the URI - we could change it later to an integer ID if we want.
Rust-side code passes the workspace ID to every call to `loadPlugin`, `setupRuleConfigs`, or `lintFile`.
In CLI, it just passes `null` as the ID. There's only ever 1 workspace in CLI, so no point in the expense of passing a `String` on every call.
These functions look up the CWD from the workspace ID in the `cwds` map.
Separating these 2 concerns solves both problems listed above:
1. Plugins can be outside of the workspace's CWD (see added test).
2. `getResponsibleWorkspace` is removed, solving the perf issue.
Note: The multiple hashmap lookups on each call to `lintFile` remain a perf drain. This is addressed in a later PR in this stack.
overlookmotel