Collective extensions is sensitive to EOF

[som-snytt]

This allows REPL to input extensions.

Fixes #9374

[som-snytt]

Supersedes #13375

This just inlines the call to extMethod and checks EOF.

Review by @dos65

[dos65]

LGTM!

[som-snytt]

Also verified that empty extension at EOF errors correctly.

5 |
  |^
  |Extension without extension methods
1 error found

I haven't written a line counting program since I was a teenager, though I did fix some line bugs in Scala 2's Position, but I see the error is reported on a line after the last line in the file. That is with a terminal EOL, so really the "last line" is merely empty and does not itself end in EOL.

[dwijnand]

Any reason for closing this, @som-snytt?