Refactor error serialization

[ehmicky]

When a build fails, we print in the build logs.
As part of "plugin statuses" (#1223), we will also surface error information in the UI.

This PR refactors the code to ensure both can share as much logic as possible:

• the common logic to retrieve error information is put under parseError() at src/error/parse.js
• the build logs-specific logic uses this, and adds few terminal-specific logic (such as adding sub-header lines)
• an upcoming PR will use this shared logic as well, but tailored for "plugin statuses"

By having both share some common logic, we enforce a consistent experience and improve maintainability while still allowing build logs and plugin statuses to be shown in different ways.

This PR just moves lines of code around, it does not add logic.