Consider comments and bare delimiters the same as an "empty line" for purposes of hiding rendered code output of long multispans. This results in more aggressive shortening of rendered output without losing too much context, specially in `*.stderr` tests that have "hidden" comments.
* The WASI targets deal with the `main` symbol a bit differently than
native so some `codegen` and `assembly` tests have been ignored.
* All `ignore-emscripten` directives have been updated to
`ignore-wasm32` to be more clear that all wasm targets are ignored and
it's not just Emscripten.
* Most `ignore-wasm32-bare` directives are now gone.
* Some ignore directives for wasm were switched to `needs-unwind`
instead.
* Many `ignore-wasm32*` directives are removed as the tests work with
WASI as opposed to `wasm32-unknown-unknown`.
