make version(...) kwargs explicit (#36998)

- [x] Replace `version(ver, checksum=None, **kwargs)` signature with
      `version(ver, checksum=None, *, sha256=..., ...)` explicitly listing all arguments.
- [x] Fix various issues in packages:
  - `tags` instead of `tag`
  - `default` instead of `preferred`
  - `sha26` instead of `sha256`
  - etc

Also, use `sha256=...` consistently.

Note: setting `sha256` currently doesn't validate the checksum length, so you could do
`sha256="a"*32` and it would get checked as `md5`... but that's something for another PR.

var/spack/repos/builtin.mock/packages/multimethod/package.py

@@ -19,11 +19,11 @@ class Multimethod(MultimethodBase):
     homepage = "http://www.example.com/"
     url = "http://www.example.com/example-1.0.tar.gz"
 
-    version("5.0", "0123456789abcdef0123456789abcdef")
-    version("4.0", "0123456789abcdef0123456789abcdef")
-    version("3.0", "0123456789abcdef0123456789abcdef")
-    version("2.0", "0123456789abcdef0123456789abcdef")
-    version("1.0", "0123456789abcdef0123456789abcdef")
+    version("5.0", md5="0123456789abcdef0123456789abcdef")
+    version("4.0", md5="0123456789abcdef0123456789abcdef")
+    version("3.0", md5="0123456789abcdef0123456789abcdef")
+    version("2.0", md5="0123456789abcdef0123456789abcdef")
+    version("1.0", md5="0123456789abcdef0123456789abcdef")
 
     variant("mpi", default=False, description="")