`LazyRandomTypeCollection` already has fallible functions for
`getType(TypeIndex)` this exposes them in `TpiStream` and does a mini
cleanup in `LazyRandomTypeCollection`'s `GetType`.
Context: #186948 saw a crash in LLDB where we call `GetType` without
checking the type index before calling the method. In `GetType` we
called `error(std::move(EC))`, which ignores the error in release mode.
The cause was the type index `0x80000169` in an `S_LOCAL`.
We now do a soft fail in release mode - we already check the error, so
we might as well return an empty value.
Aside: The type index there feels really unusual, the type indices in
other records around the `S_LOCAL` were in a similar range. Almost looks
like some integer over-/underflow.
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