Added __magic_enum (#8436)

Fixes #8406 (and #8410).

`AddressSpace`, `MemoryScope` and `AccessQualifier` are no longer
`BaseType`.
I added a new `__magic_enum` (very similar to `__magic_type`) syntax to
be able to easily create values or these enums from the compiler. (I
don't know if it was the right way to do it, but it works and the
changes are small enough?).

I had a weird bug: `tests/language-feature/capability/address-of.slang`
was failing in `IRBuilder::_findOrEmitConstant(IRConstant& keyInst)`.
When needing a new `u64(0)`, it did not find it in the `ConstantMap`
first, but then failed to add it right after because it already existed
in the map! But this was triggered by `IRPtrType*
IRBuilder::getPtrType(IROp op, IRType* valueType, AccessQualifier
accessQualifier, AddressSpace addressSpace)`, which is a strange
coincidence... but I could not find the issue in what I did. I ended up
bumping unordered_dense, and it solved the issue (so there was a bug in
there).

1 files changed, 0 insertions, 0 deletions

diff --git a/external/unordered_dense b/external/unordered_dense
-Subproject fd80dad6285286db5be6d2588cc7ddb624db7e5
+Subproject 73f3cbb237e84d483afafc743f1f14ec53e1231