EthDebug source contents and language are mandatory

## Description

According to the EthDebug spec, a source's contents and language are required fields, but solc does not generate them. See: https://ethdebug.github.io/format/spec/materials/source

## Environment

- Compiler version: Version: 0.8.29+commit.ab55807c.Linux.g++
- Compilation pipeline (legacy, IR, EOF): IR
- Target EVM version (as per compiler settings): osaca
- Framework/IDE (e.g. Foundry, Hardhat, Remix): No
- EVM execution environment / backend / blockchain client: No
- Operating system: WSL

## Steps to Reproduce

```bash
solc --standard-json input.json --pretty-json > ouput.json
```

input.json
~~~json
{
"language": "Solidity",
"sources": {
"contract.sol": {
"content": "// SPDX-License-Identifier: MIT\npragma solidity ^0.8.29;\n\nabstract contract GreeterBase {\n function greet() public view virtual returns (string memory);\n}"
},
"interface.sol": {
"content": "// SPDX-License-Identifier: MIT\npragma solidity ^0.8.29;\n\ninterface IGreeter {\n function greet() external view returns (string memory);\n}"
}
},
"settings": {
"viaIR": true,
"debug": {
"debugInfo": [
"ethdebug"
]
},
"outputSelection": {
"*": {
"*": [
"evm.bytecode.ethdebug",
"evm.deployedBytecode.ethdebug",
"ir",
"irOptimized"
]
}
}
}
}
~~~

output.json
~~~json
{
"contracts": {
// ...
},
"ethdebug": {
"compilation": {
"compiler": {
"name": "solc",
"version": "0.8.29+commit.ab55807c.Linux.g++"
},
"sources": [
{
"id": 0,
"path": "contract.sol"
// "language": <-- missing
// "contents": <-- missing
},
{
"id": 1,
"path": "interface.sol"
// "language": <-- missing
// "contents": <-- missing
}
]
}
},
"sources": {
"contract.sol": {
"id": 0
},
"interface.sol": {
"id": 1
}
}
}
~~~

Start by reproducing the issue with solc --standard-json using the provided input.json and inspect the generated ethdebug compilation.sources entries. Compare the output with the EthDebug source requirements; done means each source entry contains its required language and contents fields.

Written by the indexing model from the issue text.