Code completion in the source editor

[ktraunmueller]

Features

• Code completion should be installation-aware, i.e., the catalog of commands and document classes should be updated whenever new packages are installed.
• Code completion should only suggest commands provided by packages currently included in the document.
• When editing the document class line, only installed document classes should be suggested.
• Options declared by packages (via \DeclareOption) should be provided in a context-sensitive way in the completion suggestions.
• Code completion results should contain links to external documentation. For built-in LaTeX commands, link to https://latex2e.org. For other packages, link to CTAN (e.g., https://ctan.org/pkg/geometry for the geometry package).