ICE in `MagicVariableDeclaration::functionType` when `abi` is subscripted in a state variable array size

The compiler panics with `Solidity assertion failed` in [`libsolidity/ast/AST.h:1398`](https://github.com/ethereum/solidity/blob/9be66192f9db40e5a43f71fc78e06b2f35e9ccdd/libsolidity/ast/AST.h#L1398) inside `MagicVariableDeclaration::functionType()` when `abi` is used as a subscriptable expression in the size of a state variable array declaration.

MRE:
```solidity
contract C { uint[uint(abi("")[0])] x; }
```

Reproduce: save as `mre.sol`, run `solc --bin mre.sol`.

Output:
```
Internal compiler error:
/solidity/libsolidity/ast/AST.h(1398): Throw in function virtual const solidity::frontend::FunctionType* solidity::frontend::MagicVariableDeclaration::functionType(bool) const
Dynamic exception type: boost::wrapexcept
std::exception::what: Solidity assertion failed
[solidity::util::tag_comment*] = Solidity assertion failed
```

Expected behavior: a type error explaining that `abi` cannot be subscripted or used as a function.

Also reproduces with `abi("").length` as the array size.

Git commit: 9be66192f
solc 0.8.35-develop.2026.4.18+commit.9be66192.Linux.g++

Start by reproducing the issue with the provided mre.sol input using solc --bin mre.sol, then inspect libsolidity/ast/AST.h:1398 and the MagicVariableDeclaration::functionType() path. Check both the subscripted abi expression and abi("").length case. Done means the compiler reports a type error explaining that abi cannot be subscripted or used as a function instead of panicking.

Written by the indexing model from the issue text.