feat: pathname in SSR APIs when in develop (#12995)

Update the docs for this change: #9792.
It's not a breaking change.
It also adds the pathname to `onRenderBody` and `onPreRenderHTML` in developer.

packages/gatsby/cache-dir/api-ssr-docs.js

@@ -3,6 +3,7 @@
  * Redux, css-in-js libraries, etc. that need custom setups for server
  * rendering.
  * @param {Object} $0
+ * @param {string} $0.pathname The pathname of the page currently being rendered.
  * @param {function} $0.replaceBodyHTMLString Call this with the HTML string
  * you render. **WARNING** if multiple plugins implement this API it's the
  * last plugin that "wins". TODO implement an automated warning against this.
@@ -99,6 +100,7 @@ exports.onRenderBody = true
  * replace head components to be rendered in your `html.js`. This is useful if
  * you need to reorder scripts or styles added by other plugins.
  * @param {Object} $0
+ * @param {string} $0.pathname The pathname of the page currently being rendered.
  * @param {Array<ReactNode>} $0.getHeadComponents Returns the current `headComponents` array.
  * @param {function} $0.replaceHeadComponents Takes an array of components as its
  * first argument which replace the `headComponents` array which is passed

packages/gatsby/cache-dir/develop-static-entry.js

@@ -84,6 +84,7 @@ export default (pagePath, callback) => {
     setPreBodyComponents,
     setPostBodyComponents,
     setBodyProps,
+    pathname: pagePath,
   })
 
   apiRunner(`onPreRenderHTML`, {
@@ -93,6 +94,7 @@ export default (pagePath, callback) => {
     replacePreBodyComponents,
     getPostBodyComponents,
     replacePostBodyComponents,
+    pathname: pagePath,
   })
 
   const htmlElement = React.createElement(Html, {