Read and parse LSIF references

In order to be able to "Find references" of a given range or definition, we need to be able to read references items from the LSIF file.

This will then be written to the JSON file for each range via references property.

The property will look something like:

"references": [
  {
    "path": "main.go#L7"
  }
]

Each reference will be an object with path property. The path property will point to the exact line where it is being used.

This is currently behind a feature flag (code_navigation_references) which will set ProcessLsifReferences header to true when enabled. If false, the references won't be read and generated.

• Feature Flag MR: gitlab!35626 (merged)
• Pre-requisite MR: !523 (merged)

Related to gitlab#217392 (closed).