fix(runtime): add compressed {&packpath}/start/*/pack/*[/after] representation to &rtp
by suggestion by at-tpope
Summary:
We can add XDG_DATA_DIR/nvim/site/pack/*/start/* (et al) as an unexpanded wildchar to &rtp which keeps it both short and explicit and still supporting globpath(&rtp, ...).
ref #15101
site packages must be sourced before user config
NOTE: we only consider dirs exactly matching "after" to be an AFTER dir.
vim8 considers all dirs like "foo/bar_after", "Xafter" etc, as an
"after" dir in SOME codepaths not not in ALL codepaths.
The order should be:
XDG_CONFIG_HOME/nvim
XDG_DATA_HOME/nvim/site/pack/foo/start/bar/
XDG_CONFIG_HOME/nvim/after
XDG_DATA_HOME/nvim/site/pack/foo/start/bar/after
Now remove the addition of "start/*" packages in 'packpath' as
explicit items in 'runtimepath'. This avoids 'runtimepath' from becoming
very long when using a lot of plugins as packages.
To get the effective search path as a list, use |nvim_list_runtime_paths()|
ftdetect files in start packages are sourced once from the :runtime
command in filetype.vim and once when packages are loaded. Change the
package loading logic to only source ftdetect files for opt packages to
avoid this duplication.
