Instead of generating IL2045 use the lazy marking of attributes and preserve otherwise referenced attributes

Currently if an attribute is marked for removal of its instances via the `RemoveAttributeInstances` internal annotation and then the attribute type is directly referenced from the code (for example via `typeof(MyAttribute)`), the linker will generate warning IL2045 saying that this is potentially problematic as the attribute instances are being removed.

To mitigate the problem the developer can either:
* Suppress the warning via `UnconditionalSuppressMessage` attribute, assuming the code referencing the attribute type will continue working as expected (or if the change in behavior is acceptable).
* Force-include the attribute instances by marking the attribute type as preserved in a link descriptor XML file (anywhere in the app)

We could effectively remove the need for IL2045 by implementing attribute removal via the functionality already present in `MarkStep` for `--used-attribs-only`:
* If we see an attribute that is of a "removable type", don't mark it, just add it into the lazily marked list.
* If the attribute type ended up getting marked (e.g. because there was a `typeof`), mark the attributes as well (this is what the `--used-attribs-only` does too, but the twist would be that we don't let it happen to random attributes, only to those that are in the list).

See https://github.com/dotnet/runtime/issues/39707#issuecomment-662314499 for the discussion leading to this proposal.