Now we give each sheet its own interpreter and realm, and only make them
share the VM.
This is to prepare for the next commit, which will be refactoring a
bunch of things to propagate exceptions via ThrowCompletionOr<T>.
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 will make constructing (and destructing) Positions a lot cheaper
(as it no longer needs to ref() and unref() a String).
Resulted from #5483, but doesn't fix it.
(...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.
