langchain: globals fix (#21281)

Issue: functions from `globals`, like the `get_debug` are placed in the
init.py file. As a result, they don't listed in the API Reference docs.
[See
this](https://langchain-9jq1kef7i-langchain.vercel.app/v0.2/docs/how_to/debugging/#set_debugtrue)
and [broken
this](https://api.python.langchain.com/en/latest/globals/langchain.globals.set_debug.html).
Change: moved code from init.py into the `globals.py` file and removed
`globals` directory. Similar to: #21266
BTW `globals` in core implemented exactly inside a file not inside a
folder.