AtStyleRule being a subclass of QualifiedStyleRule was causing
problems when trying to distinguish between them. Combining them
and then distinguishing between them with a Type enum makes that
check simpler, and is in line with how similar checks are done
elsewhere in the parser.
Previously these were all passed around by value, but some of them
(StyleComponentValueRule and StyleBlockRule) want to include each
other as fields, so this had to change.
We had some inconsistencies before:
- Sometimes "The", sometimes "the"
- Sometimes trailing ".", sometimes no trailing "."
I picked the most common one (lowecase "the", trailing ".") and applied
it to all copyright headers.
By using the exact same string everywhere we can ensure nothing gets
missed during a global search (and replace), and that these
inconsistencies are not spread any further (as copyright headers are
commonly copied to new files).
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
