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 *
This particularly affects the insertion steps and the removed steps.
The insertion steps no longer take into the parent that the node
was inserted to, as per the spec. Due to this, I have renamed the
function from "inserted_into" to simply "inserted". None of the
users of the insertion steps was using it anyway.
The removed steps now take a pointer to the old parent instead of
a reference. This is because it is optional according to the spec
and old parent is null when running the removal steps for the
descendants of a node that just got removed.
This commit does not affect HTMLScriptElement as there is a bit
more to that, which is better suited for a separate commit.
Also adds in the adopted steps as they will be used later.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
