Implement bun why (#20847)

Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

docs/cli/why.md

@@ -0,0 +1,67 @@
+The `bun why` command explains why a package is installed in your project by showing the dependency chain that led to its installation.
+
+## Usage
+
+```bash
+$ bun why <package>
+```
+
+## Arguments
+
+- `<package>`: The name of the package to explain. Supports glob patterns like `@org/*` or `*-lodash`.
+
+## Options
+
+- `--top`: Show only the top-level dependencies instead of the complete dependency tree.
+- `--depth <number>`: Maximum depth of the dependency tree to display.
+
+## Examples
+
+Check why a specific package is installed:
+
+```bash
+$ bun why react
+react@18.2.0
+  └─ my-app@1.0.0 (requires ^18.0.0)
+```
+
+Check why all packages with a specific pattern are installed:
+
+```bash
+$ bun why "@types/*"
+@types/react@18.2.15
+  └─ dev my-app@1.0.0 (requires ^18.0.0)
+
+@types/react-dom@18.2.7
+  └─ dev my-app@1.0.0 (requires ^18.0.0)
+```
+
+Show only top-level dependencies:
+
+```bash
+$ bun why express --top
+express@4.18.2
+  └─ my-app@1.0.0 (requires ^4.18.2)
+```
+
+Limit the dependency tree depth:
+
+```bash
+$ bun why express --depth 2
+express@4.18.2
+  └─ express-pollyfill@1.20.1 (requires ^4.18.2)
+     └─ body-parser@1.20.1 (requires ^1.20.1)
+     └─ accepts@1.3.8 (requires ^1.3.8)
+        └─ (deeper dependencies hidden)
+```
+
+## Understanding the Output
+
+The output shows:
+
+- The package name and version being queried
+- The dependency chain that led to its installation
+- The type of dependency (dev, peer, optional, or production)
+- The version requirement specified in each package's dependencies
+
+For nested dependencies, the command shows the complete dependency tree by default, with indentation indicating the relationship hierarchy.

docs/nav.ts

@@ -176,6 +176,9 @@ export default {
     page("cli/pm", "`bun pm`", {
       description: "Utilities relating to package management with Bun.",
     }),
+    page("cli/why", "`bun why`", {
+      description: "Explains why a package is installed in your project.",
+    }),
     page("install/cache", "Global cache", {
       description:
         "Bun's package manager installs all packages into a shared global cache to avoid redundant re-downloads.",