fix: show contents of definition in preview window

[hftsin]

For non-ts LSP response, it only shows the filename, line number and column number. This PR enhance the preview window by showing the contents of definitions and references.

[w0rp]

Very interesting. I'll have to try this out.

[Copilot]

Pull Request Overview

This PR enhances the preview window by including the content of definitions and references for non-TypeScript LSP responses. It updates test assertions to include a new key ("use_relative_paths"), introduces a helper function for safely reading a file’s specific line, and adjusts formatting functions in both definition and references modules to display the retrieved content.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/test_go_to_definition.vader	Updated test assertions to include "use_relative_paths" in the preview details
test/test_find_references.vader	Added an empty 'match' key to reference items for content consistency
autoload/ale/util.vim	Introduced SafeReadFileLine to read a particular line from a file safely
autoload/ale/references.vim	Modified formatting function to include file content in the reference preview
autoload/ale/definition.vim	Modified formatting function and command handler to incorporate file content and relative path options

[Copilot]

If performance becomes an issue for large files, consider using a method that reads only the target line rather than reading all lines up to it.

Suggested change

	let l:content = readfile(a:filename, '', a:line)[-1]
	let l:content = getline(a:line, a:filename)

[rymdbar]

I assume this PR may be closed as the same functionality was merged with #5001?

[hftsin]

I revise this PR to show definitions / implementations in preview window. E.g., show all implementations for go interface,

@w0rp pls help review 🙏