Update testsuite (for SIMD) (#1373)
Lots of changes necessary to make this work, as well as some bug fixes.
The main change is allowing `nan:canonical` and `nan:arithmetic` as a
possible value for each lane of a `v128`. This needs to propogate
through the parser, IR, the JSON format, and the spec interpreter.
This also changes the format of the spec JSON file, where a SIMD value
is now stored as a list of values instead of a single u128:
```
{"type": "v128", "lane_type": "i32", "value": ["0", "0", "0", "0"]}
```
Since the lane type can be `i8` and `i16`, these types can now be used
in more places (not just the decompiler). They'll be used for the GC
proposal too (for packed values), so I've updated them to use the binary
value specified for that proposal.
Here are the actual SIMD fixes:
* SIMD lanes are malformed if they don't match the binary format, but
invalid if they are smaller than the lane width. For example,
`i8x16.extract_lane_s` is malformed if the lane is >= 256, because the
lane is stored as a byte. But it is invalid if the lane is >= 16.
* The `i8x16.narrow_i16x8_u`, `i16x8.narrow_i32x4_u` and
`i64x2.load_32x2_u` instructions were not handling sign-extension
propoerly.
TODO: This code is pretty clumsy now; it would be better to have a
universal `Value` and `ExpectedValue` that can be used everywhere, so
the logic doesn't need to be duplicated.
