The original attempt at this introduced a regression; this commit
reverts the revert and fixes the regression.
This reverts commit 3e151d4d77.
Fix to the regression:
flakeref: fix handling of `?dir=` param for flakes in subdirs
As reported in #419[1], accessing a flake in a subdir of a Git
repository fails with the previous commit[2] applied with the error
error: unsupported Git input attribute 'dir'
The problem is that the `dir`-param is inserted into the parsed URL if a
flake is fetched from the subdir of a Git repository. However, for the
fetching part this isn't even needed. The fix is to just pass `subdir`
as second argument to `FlakeRef` (which needs a `basedir` that can be
empty) and leave the parsedURL as-is.
Added a regression test to make sure we don't run into this again.
[1] https://git.lix.systems/lix-project/lix/issues/419
[2] e22172aaf6b6a366cecd3c025590e68fa2b91bcc,
originally 3e151d4d77
Change-Id: I2c72d5a32e406a7ca308e271730bd0af01c5d18b
