(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
Core::IODevice (which Core::File inherits from) does not have a
reasonable way to block for a line. grep was spinning on
IODevice::read_line, passing endless empty strings to the matcher
lambda. Use getline instead, which will at least block in the Kernel for
characters to be available on stdin and only return full lines (or eof)
