Org reader: parse parameter lists on unknown blocks.

The reader tries to parse the rest of the opening line of a block, e.g.,
`#+begin_myblock …`, as a parameters list. It first assumes that the parameters
are in lisp-style (`:key value`), then alternatively tries to read python-style
key-value pairs (`key=value`) and falls back to reading the entire remaining
line as a single `parameter` attribute.

This method is also applied to dynamic blocks.

Closes: #11188

test/command/11188.md

@@ -0,0 +1,80 @@
+Parsing PARAMETERS of Org-mode blocks
+
+```
+% pandoc -f org --to=native
+#+attr_html: :width 10px
+#+BEGIN_myex :this that
+huhu
+#+END_myex
+^D
+[ Div
+    ( ""
+    , [ "myex" ]
+    , [ ( "width" , "10px" ) , ( "this" , "that" ) ]
+    )
+    [ Para [ Str "huhu" ] ]
+]
+```
+
+Python-style parameters are accepted, too.
+
+```
+% pandoc -f org --to=native
+#+BEGIN_myblock width=10px
+[[image.svg][logo]]
+#+END_myblock
+^D
+[ Div
+    ( "" , [ "myblock" ] , [ ( "width" , "10px" ) ] )
+    [ Para
+        [ Span
+            ( ""
+            , [ "spurious-link" ]
+            , [ ( "target" , "image.svg" ) ]
+            )
+            [ Emph [ Str "logo" ] ]
+        ]
+    ]
+]
+```
+
+The fallback is to put the remainder of the line into a `parameters`
+attribute.
+
+```
+% pandoc -f org --to=native
+#+BEGIN_myblock these are parameters in an unsupported format
+/OK/
+#+END_myblock
+^D
+[ Div
+    ( ""
+    , [ "myblock" ]
+    , [ ( "parameters"
+        , "these are parameters in an unsupported format"
+        )
+      ]
+    )
+    [ Para [ Emph [ Str "OK" ] ] ]
+]
+```
+
+Also works on dynamic blocks.
+
+```
+% pandoc -f org --to=markdown
+#+BEGIN: clocktable :scope subtree :maxlevel 3
+#+CAPTION: Clock summary at [2025-10-18 Sat 17:23]
+| Headline     | Time   |
+|--------------+--------|
+| *Total time* | *0:00* |
+#+END:
+^D
+::: {.clocktable scope="subtree" maxlevel="3"}
+  Headline         Time
+  ---------------- ----------
+  **Total time**   **0:00**
+
+  : Clock summary at \[2025-10-18 Sat 17:23\]
+:::
+```