Lightroom doesn't currently support importing from Apple Photos library. Therefore, the only way I know to get to the files in the Photos Library is to do so manually.
First you'll need to select the Apple 'Photo Library' in your 'Pictures' folder then right click to open the context menu. On context menu you'll see an item named 'Show Packages Contents'. Click on this to open the Photos Library. In the Photos Library you'll find a 10 or so folders, one of which should be named 'Masters'. Copy this folder to the Pictures folder folder. This is where it can get messy. Apple stores your files in dozens, if not hundreds, of Hex numerically named folders. If you want all of the photos to be in their correctly named album etc then your out of luck. The best you can do is import the contents of this copy of the Masters folder into Lightroom using normal import procedure (make sure 'Include Subfolders' is checked in top left corner of import window). You can rename the Apple folders from Lightroom Folder panel.
I am in the same situation. This is simply unacceptable. I have 45,000 RAW images compiled over 10 years organized by year and photo shoot. There MUST be a way that LR can import this and maintain the current organization. Otherwise, I and many others will have a disaster on our hands.