Previously type sizes would be inconsistently sourced from either the LLVM type
or the FixedTypeInfo, depending on the call site. This was problematic because
TypeInfo operates with a resolution of whole bytes, which means that types such
as i1 would get a reported as having a size of 8. This patch now asserts that
all occurrences of the same type have the same size as the first, cached
occurence.
To avoid triggering the cached type verification assertion, this patch avoids
caching of storage-sized containers. It also removes the unique identifier from
forward declarations, which could lead to type confusion during LTO.
rdar://102367872
* Make the underlying builtins for FP + Vector match Integer.
For stdlib integer types, these are named `_value` and `init(_ _value: Builtin.xxx)`. This patch adopts the same scheme for stdlib floating point and SDK overlay vector types, and removes a legacy init for integers that was only needed to support them. There should be no changes visible outside of the stdlib, and no functional change within the stdlib; the naming of some implementation details is simply more uniform now.
