Detect MethodImplOptions.Async (0x2000) in ILReader and unpack Task/Task<T>
return types so the IL Leave value and function.AsyncReturnType match the
source signature. Add CSharp15_0 (Preview also bumped to 1500) and a
RuntimeAsync setting (default on, gated to >=CSharp15_0), expose it in the
Languages dropdown, mask the synthetic MethodImplAsync bit out of the
decompiled [MethodImpl], and add a .runtimeasync test suffix.
The C# 9 IntPtr / UIntPtr guard in IsBinaryCompatibleWithType read
type.Kind is not TypeKind.NInt or TypeKind.NUInt
which parses as `(is not NInt) or (is NUInt)` — true unless
Kind == NInt. The intent (per the surrounding comment "but not nint
or C# 11 IntPtr") is "Kind is neither NInt nor NUInt", which needs
parentheses around the alternation:
type.Kind is not (TypeKind.NInt or TypeKind.NUInt)
Effect: when Kind == NUInt the branch no longer mistakenly applies
the C# 9 IntPtr-only restrictions (suppressing compound assignment
without nint, disallowing shifts).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
CopyPropagation will replace `ref StructWithStringField reference = ref array[0];` with:
```
var x = array;
var y = 0;
```
and then every use of `reference` is replaced with `x[y]`.
This lets us avoid rough locals while preserving the semantics in every case except that we re-order when a NullReferenceException/IndexOutOfRangeException occurs.
This way we avoid having to extract later, as we will never inline if the `isinst` argument if this could result in it being unrepresentable in C#.
This commit also refactors inlining restrictions to avoid requiring special cases in ILInlining itself.
But when making this change, I discovered that this broke our pattern-matching tests, and that the weird IL with double `isinst` is indeed generated by the C# compiler for `if (genericParam is StringComparison.Ordinal)` style code. So instead we also allow `isinst` with a `box(expr-without-side-effects)` argument to be represented with the `expr is T ? (T)expr : null` emulation.