Support source-context resolution from multiple files

[vaind]

Historically, only source-bundles contained sources for source-context. Nowadays, you can also have them in Portable PDBs, whether as embedded, or as links. In the future, other formats may follow.

In order to resolve source context as best as we can, we should not limit resolution to a single debug file that reports has_sources() = true but instead try to match each of them until a match is found. Alternatively, they should be combined. This resolution could be cached if needed.

[vaind]

This came up in getsentry/sentry#60236

We'd need to change how the candidates are looked up. Doesn't seem so hard to do but maybe I'm missing something:

symbolicator/crates/symbolicator-native/src/symbolication/module_lookup.rs

Lines 312 to 333 in 2474a74

	let objects = objects.clone();
	let find_request = FindObject {
	filetypes: FileType::sources(),
	purpose: ObjectPurpose::Source,
	identifier: object_id_from_object_info(&entry.object_info.raw),
	sources: self.sources.clone(),
	scope: self.scope.clone(),
	};
	let fut = async move {
	let FindResult { meta, candidates } = objects.find(find_request).await;
	let source_object = match meta {
	Some(meta) => match meta.handle {
	Ok(handle) => objects.fetch(handle).await,
	Err(err) => Err(err),
	},
	None => Err(CacheError::NotFound),
	};
	(idx, source_object, candidates)
	};

Notably from objects.find() docs: " /// Fetches matching objects and returns the metadata of the most suitable object." - it returns a single object.