Delay validation of elem init expressions until validation time (#1730)
Doing validation at parse time means we cannot run tests which
included invalid instruction in the elem init expressions.
For example. the updated test suite repo contains tests such as this:
```
(assert_invalid
(module
(table 1 funcref)
(elem (i32.const 0) funcref (item (i32.add (i32.const 0) (i32.const 1))))
)
"constant expression required"
)
```
There we have an illegal instruction sequence in the init expresssion.
However, in order to run this test we need to be able to process it with
wast2json first which means it at least has to parse correctly.
This change removes the `ElemExpr` and `ElemExprKind` types from the IR
and instead just stores elem init expressions as `ExprList` like we do
for global init expressions. This expression list can then be validated
but crucially can also be invalid.
This technique matches the existing `OnDataSegmentInitExpr_Other` and
`OnGlobalInitExpr_Other` and indeed it seem that it was indented to
work this way since the `OnElemSegmentElemExpr_Other` already existed
(unused) in the codebase.
wabt
68fe76c6 - Delay validation of elem init expressions until validation time (#1730)
