Add babel plugin to internal deps

[Tobbe]

Trying to make test-project generation work

Currently erroring out on

Error in script: Cannot find module '@babel/plugin-proposal-private-methods'
Require stack:
- /Users/dac09/Experiments/xxx/node_modules/@babel/core/lib/config/files/plugins.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/core/lib/config/files/index.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/core/lib/index.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/register/lib/worker/babel-core.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/register/lib/worker/handle-message.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/register/lib/worker-client.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/register/lib/node.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/register/lib/nodeWrapper.js
- /Users/dac09/Experiments/xxx/node_modules/@babel/register/lib/index.js
- /Users/dac09/Experiments/xxx/node_modules/@redwoodjs/internal/dist/build/babel/common.js
- /Users/dac09/Experiments/xxx/node_modules/@redwoodjs/internal/dist/build/babel/api.js
- /Users/dac09/Experiments/xxx/node_modules/@redwoodjs/cli/dist/commands/execHandler.js
- Did you mean "@babel/plugin-transform-private-methods"?

[jtoar]

LGTM, maybe we could remove it from core too?