Fix false-positive `"use cache"` misplacement error (#79151)
This fixes an error where we incorrectly showed the following compiler
error when using Turbopack:
```sh
Ecmascript file had an error
> 1 | 'use cache'
| ^^^^^^^^^^^
2 |
3 | import { useStuff } from './client-module'
4 |
The "use cache" directive must be at the top of the file.
```
The directive was regarded as not being at the top of the file, because
the React transform (`EcmascriptInputTransform::React`) injects a
variable declaration for React Refresh (e.g. `var _s =
__turbopack_context__.k.signature`) at the top of the file, before the
`"use cache"` directive.
We can fix this by ensuring that the server action transform (should
really be called "server _function_ transform") runs first.
As a consequence, the transform now needs to be able to parse JSX AST
nodes, which was already explicitly implemented.
closes NAR-130
