Because TokenStream is copied around a lot, moving it to use
`StringRef` removes _a lot_ of allocations per `Opt` in the parser.
Args are not copied around much, but changing them as well makes it
obvious that they do not participate in the ownership.
The changes add up to removing ~180 allocations for "empty"
invocation of the test binary.
(`./tests/ExtraTests/NoTests --allow-running-no-tests -o /dev/null`
is down to 317 allocs)
This enables its inlining even without LTO, which in turns enables
callers to determine that two StringRefs are unequals with simple
comparison of two numbers, without any function calls.
This commit also strips the old copyright comment header in touched
files, as those will also be replaced with a more standardized and
machine-friendly version.
Martin Hořeňovský
Lars Toenning