Fixes for installing from outside a dists directory

Use the stable names instead of local file paths when generating file
ids. This way those ids no longer depend on the current working
directory. Previously we used  the path like "./lib/Foo.pm6" for
generating the id and would end up with a different id if installing the
file by using e.g. "modules/Foo/lib/Foo.pm6".

Only affects newly installed dists.

src/core/CompUnit/Repository/Installation.pm

@@ -134,7 +134,8 @@ sub MAIN(:$name is copy, :$auth, :$ver, *@, *%) {
         # "provides" or just "files".
         for %sources.kv -> $name, $file is copy {
             $file           = $is-win ?? ~$file.subst('\\', '/', :g) !! ~$file;
-            my $id          = self!file-id($file, $dist-id);
+            # $name is "Inline::Perl5" while $file is "lib/Inline/Perl5.pm6"
+            my $id          = self!file-id($name, $dist-id);
             my $destination = $sources-dir.child($id);
             self!add-short-name($name, $dist);
             $dist.provides{ $name } = {
@@ -171,7 +172,8 @@ sub MAIN(:$name is copy, :$auth, :$ver, *@, *%) {
 
         for %resources.kv -> $name, $file is copy {
             $file              = $is-win ?? ~$file.subst('\\', '/', :g) !! ~$file;
-            my $id             = self!file-id($file, $dist-id) ~ '.' ~ $file.IO.extension;
+            # $name is 'libraries/p5helper' while $file is 'resources/libraries/libp5helper.so'
+            my $id             = self!file-id($name, $dist-id) ~ '.' ~ $file.IO.extension;
             my $destination    = $resources-dir.child($id);
             $dist.files{$name} = $id;
             copy($file, $destination);