feat(document): deprecate the four drawing element types

[andiwand]

🤖 Generated with Claude Code

The deprecation half of #773. Nothing changes at runtime, and no emitted html
moves — this only marks what the follow-up removes, so consumers get a release
that warns before the one that breaks.

What is deprecated

• ElementType::rect, ::line, ::circle, ::custom_shape
• odr::Rect, odr::Line, odr::Circle, odr::CustomShape
• Element::as_rect(), ::as_line(), ::as_circle(), ::as_custom_shape()

Mirrored in the bindings: @Deprecated on the Java classes, ElementType
constants and Element.as* methods; DEPRECATED_MSG_ATTRIBUTE on the ObjC
interfaces and ODRElementType values; docstrings on the pybind classes,
enumerators and methods. Wasm binds no element types, so it is untouched.

The replacement lands in the stacked breaking PR: Frame gains a
ShapeType shape_type() discriminator plus the geometry the four classes
carried, and the odf parser maps every draw:* shape onto it. frame is
already the generic-shape element in five of the six engines — only odf ever
produced the other four.

ODR_DEPRECATED

[[deprecated]] on an api the library itself renders through would fail CI,
which builds with -Werror. So definitions.hpp gains

#ifdef ODR_INTERNAL_BUILD
#define ODR_DEPRECATED(message)
#else
#define ODR_DEPRECATED(message) [[deprecated(message)]]
#endif

and ODR_INTERNAL_BUILD is set PRIVATE on odr, odr_test, odr_jni,
pyodr_core and odr_apple — the library and its own mirrors, which have to
keep serving what they deprecate. Consumers building against the installed
headers get the attribute. ODRDocumentElement.mm needs one file-scope
-Wdeprecated-declarations pragma on top, for the ObjC attributes the macro
does not reach.

This also gives the repo's existing doc-comment-only deprecations
(html.hpp, global_params.hpp) somewhere to grow a real attribute.

Verified

• -Werror build with -DODR_TEST=ON -DODR_JNI=ON -DODR_PYTHON=ON: clean.
• ODRDocumentElement.mm syntax-checked with -Werror separately (the apple
  target is not in that job).
• A consumer TU compiled without ODR_INTERNAL_BUILD warns on all three kinds
  of use — the enumerator, the as_* and the class.
• odr_test, odf and html filters: 67 passing.