Handle directory values of scopeUri in workspace/configuration

Handle directory values of scopeUri in  workspace/configuration

Even though scopeUri is specified to be of documentUri type, some
servers (notably pyright) insist on passing the pathname of a
directory there.  In pyright's case this is frequently useless, as the
directory is the project directory.  Nevertheless we can be lenient to
those servers by detecting whether the value is a directory and doing
the right thing.

Note that we do not (yet) support per-file configuration storage.

* lisp/progmodes/eglot.el (eglot--workspace-configuration-plist):
Rework.

Co-authored-by: João Távora <joaotavora@gmail.com>
GitHub-reference: https://github.com/joaotavora/eglot/pull/1281