[AST] Reference id to import directive alias inconsistency

## Description

Import directives allow creating of symbol aliases, for example:

```solidity
import { symbol as symbolAlias } from "./Foo.sol";
```

and source unit aliases:

```solidity
import * as unitAlias from "./Foo.sol";
```

When referencing these aliases through an Identifier node, there is an inconsistency. When referencing `symbolAlias`, referenced declaration AST node ID is the ID of the symbol itself (can be a contract definition, for example) and not the ID of the import directive, where the symbol alias was declared.

When referencing `unitAlias`, referenced declaration AST node ID points to the import directive, where the unit alias was declared and not to the source unit itself.

## Environment

- Compiler version: 0.8.19
- Target EVM version (as per compiler settings): latest
- Framework/IDE (e.g. Truffle or Remix): n/a
- EVM execution environment / backend / blockchain client: n/a
- Operating system: Linux

## Steps to Reproduce

Please see the example here: https://github.com/michprev/solc-ast-import-alias-inconsistency. It contains generated ASTs of all files.

In file A, `Base` (https://github.com/michprev/solc-ast-import-alias-inconsistency/blob/c399cdcda566c5e2b86472422ac5ca47425d8b0b/contracts/A.sol#L8) is an Identifier node and it's referenced declaration ID points to the import directive (https://github.com/michprev/solc-ast-import-alias-inconsistency/blob/c399cdcda566c5e2b86472422ac5ca47425d8b0b/contracts/A.sol#L4).

In file B, `Base2` (https://github.com/michprev/solc-ast-import-alias-inconsistency/blob/c399cdcda566c5e2b86472422ac5ca47425d8b0b/contracts/B.sol#L8) is an Identifier node and it's referenced declaration ID points to the contract definition (https://github.com/michprev/solc-ast-import-alias-inconsistency/blob/c399cdcda566c5e2b86472422ac5ca47425d8b0b/contracts/Base.sol#L4-L6).

This introduces inconsistency - an import directive is referenced from a source unit alias but is not referenced from a symbol alias.

Start with the linked reproduction repository and inspect the generated ASTs for contracts/A.sol and contracts/B.sol, especially the Identifier nodes and their referenced declaration IDs. Trace the Solidity compiler's AST handling for symbol and source-unit import aliases; the fix is complete when both alias forms follow consistent referenced-declaration semantics and the AST examples demonstrate that behavior.

Written by the indexing model from the issue text.