Add UI Picker to apply CRs to lines
User Story: As a Forum Member, I need to be able to associate specific portions of a page to my Change Requests so that I can communicate the context of my CR more effectively.
Background
This feature, referred to as "Tagging" in Plato, is a key feature in effectively using the CR panel to review documents. It is significantly easier to explain a change if the text can be referenced specifically, and in the absence of such tooling users will reinvent it anyway by stating the surrounding line context / section numbers in their Rationale anyway.
We won't be able to get this implemented until some kind of source mapping exists in the Antora compilation output, and that work is being done in #16.
Strategy
The exact mechanisms can be a dealer choice, but the general theory is to be able to extend the "Applies To" form element to enable selecting particular lines of the shown document. Perhaps it can be a mode switch -- toggle on, then select which lines apply, then save your selections. Or maybe clicking on the source document while the CR panel is open automatically adds it without the extra step. Maybe something else; this will need to be determined experimentally.
It is expected that CRs can be applied to multiple different source lines. These may not be contiguous, and may not even be in the same source file. However, to contain the scope of this issue, they will all need to come from the same source repository.
These line numbers will need to be included in the generate issue Markdown, preferably with a link to view/edit them quickly.
Also, the line number are only intended to be valid as of the time they were first associated. It is known that any changes to the source document will make line numbers obsolete, but that sophistication will be handled in a different issue (#18).
Acceptance Criteria
- A user has a mechanism to associate their CR to one or more source lines of AsciiDoc -- without needing to look up the source file manually
- The links are included in any Issue Markdown