Reworked t/base/lex.t to use less hardcoded test numbers.

The later two thirds of the file now consistently use $test, which
should make future tweaks to the file simpler.
toke.c, S_scan_ident: Skip over newlines as well as spaces and tabs.

Not doing this lead to some bugs, such as 'eval "*{\nOIN}"'
returning a glob for "\nOIN" rather than just "OIN", or
'eval "\${\cT\n}"' giving spurious syntax errors.

Note however that this is not a full fix, since that latter
test case still fails outside of an eval.
[perl #119123] disallow literal control character variables

This introduces a deprecation warning on things like $^T, where ^T
is a literal control character in the source code.