doc: make all manpages with Doxygen

Use (fixed-up) Doxygen manpage output for all program & module manpages.

This also allows formatting the manual pages properly in the HTML docs.

The Markdown pages work properly only with Doxygen >= 1.9.7, older
versions put them to wrong place in the HTML docs.

doc/dox/programs/pw-dot.1.md

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+\page page_man_pw-dot_1 pw-dot
+
+The PipeWire dot graph dump
+
+# SYNOPSIS
+
+**pw-dot** \[*options*\]
+
+# DESCRIPTION
+
+Create a .dot file of the PipeWire graph.
+
+The .dot file can then be visualized with a tool like **dotty** or
+rendered to a PNG file with `dot -Tpng pw.dot -o pw.png`.
+
+# OPTIONS
+
+\par -r | \--remote=NAME
+The name the remote instance to connect to. If left unspecified, a
+connection is made to the default PipeWire instance.
+
+\par -h | \--help
+Show help.
+
+\par \--version
+Show version information.
+
+\par -a | \--all
+Show all object types.
+
+\par -s | \--smart
+Show linked objects only.
+
+\par -d | \--detail
+Show all object properties.
+
+\par -o FILE | \--output=FILE
+Output file name (Default pw.dot). Use - for stdout.
+
+\par -L | \--lr
+Lay the graph from left to right, instead of dot's default top to
+bottom.
+
+\par -9 | \--90
+Lay the graph using 90-degree angles in edges.
+
+# AUTHORS
+
+The PipeWire Developers <$(PACKAGE_BUGREPORT)>;
+PipeWire is available from <$(PACKAGE_URL)>
+
+# SEE ALSO
+
+\ref page_man_pipewire_1 "pipewire(1)",
+\ref page_man_pw-cli_1 "pw-cli(1)",
+\ref page_man_pw-mon_1 "pw-mon(1)",