Add line number and column to --standard-json sourceLocation

## Abstract

I am integrating `solc` as a linter into `vim`, using the `--standard-json` interface. Like most editors, Vim expects linter output to include precise **line** and **column** information for errors and warnings. Currently, `solc` only provides character offsets (`start` and `end`) in its `sourceLocation` object, which makes editor integration inefficient and error-prone.

## Motivation

Getting accurate line and column numbers from the following output requires external logic:

```json
{
"start": 1296,
"end": 1319,
"file": "contracts/BaseCollection.sol"
}
```

To convert offsets to line/column:

* The editor must read and parse the entire file.
* It must compute line breaks and offsets manually to map positions.

This adds complexity to every tool that consumes `solc` diagnostics, slows down linting workflows, and increases the potential for mismatches between source code views and diagnostic locations.

## Specification

Enhance the `sourceLocation` object in `--standard-json` output by optionally including the following keys:

```json
{
"file": "contracts/BaseCollection.sol",
"start": 1296,
"end": 1319,
"line_start": 42,
"column_start": 5,
"line_end": 43,
"column_end": 2
}
```

Where:

* `line_start` and `column_start` refer to the position of the `start` offset.
* `line_end` and `column_end` refer to the position of the `end` offset.
* All values are 1-based (like most editors and diagnostics protocols).

This format is compatible with common LSP, ALE, and IDE conventions.

## Backwards Compatibility

This proposal is fully backward-compatible:

* Existing tools using `start` and `end` will continue to work as-is.
* Tools that support `line_start`, `column_start`, etc., can use them directly for better UX.
* Fields are optional and additive.

Although some rigid tools may validate the schema strictly, it is reasonable to expect that long-term support for structured JSON diagnostics will allow for optional metadata fields.

Start at the solc --standard-json diagnostic output that constructs the sourceLocation object. Trace how start and end offsets are produced, then identify the existing standard-json diagnostics checks to extend. Done means the output optionally includes the four 1-based line and column fields while preserving start, end, and file.

Written by the indexing model from the issue text.