Adds functions for accessing git index content and working tree files:
- get_index_content() retrieves file from staging area via :0:path
- get_working_content() reads file directly from disk
- file_exists_in_index() checks if file is staged
- file_exists_at_revision() checks if file exists at given revision
Compares current buffer against any git revision (default HEAD), opens result
with full diffs.nvim syntax highlighting. Follows fugitive convention:
:Gdiff/:Gvdiff open vertical split, :Ghdiff opens horizontal split.
Apply treesitter highlighting to diff metadata lines (diff --git, index,
---, +++) using the diff language parser. Header info is attached only
to the first hunk of each file to avoid duplicate highlighting.
Based on PR #52 by @phanen with fixes:
- header_lines now only contains diff metadata, not hunk content
- header info attached only to first hunk per file
- removed arbitrary hunk count restriction
