Change CLIF shuffle to validate lane indices (#5995)

* Change CLIF `shuffle` to validate lane indices

Previously the CLIF `shuffle` instruction did not perform any validation
on the lane shuffle mask and specified that out-of-bounds lanes always
returned 0 as the value. This behavior though is not required by
WebAssembly which validates that lane indices are always in-bounds.
Additionally since these are static immediates even other code
generators should be able to verify that the immediates are in-bounds.

As a result this commit updates the definition of the `shuffle`
instruction to specify that all byte immediates must be in-bounds in the
range of [0, 32). The verifier has been updated and some test cases have
been removed that were testing this functionality.

Closes #5989

* Only generate valid shuffle immediates in fuzzer

cranelift/filetests/filetests/runtests/simd-shuffle.clif

@@ -14,13 +14,6 @@ block0(v0: i8x16, v1: i8x16):
 }
 ; run: %shuffle_i8x16([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16], [17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32]) == [4 1 32 27 5 7 13 12 24 14 25 5 3 16 18 6]
 
-function %shuffle_zeros(i8x16, i8x16) -> i8x16 {
-block0(v0: i8x16, v1: i8x16):
-    v2 = shuffle v0, v1, [3 0 32 255 4 6 12 11 23 13 24 4 2 97 17 5]
-    return v2
-}
-; run: %shuffle_zeros([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16], [17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32]) == [4 1 0 0 5 7 13 12 24 14 25 5 3 0 18 6]
-
 function %shuffle1(i8x16) -> i8x16 {
 block0(v0: i8x16):
     v1 = shuffle v0, v0, [8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23]