docs: refactor crawling context helper methods to have them properly documented

[B4nan]

• simplifies enqueueLinks implementation - no more child types for options
• improves types of context properties, e.g. crawler has correct type in browser crawlers
• adds jsdoc for context helpers, e.g. injectJQuery or sendRequest
• all context helpers have their "jsdoc copy", we could mauybe use @inheritDoc as an inline tag pointing to the implementation, but that would mean taking the same jsdoc - here we instead have customized version, that dont have the page param (as its context bound) and have context related examples
• contains unrelated changes in the SystemStatus to support edge case i found, we can move this outside of the PR but its not really worth having a changelog line on its own :]