Menu: Add icon property

[redstrate]

This adds an icon that is displayed to the left of the title, and is also shown for Menus are inside of a parent menu.

Closes #7791

[ogoffart]

Thanks for this much appreciated patch. Looks good to me, but I'm not the right person to judge the aesthetics, but I think it is ok for now. Could you make sure that the gallery has at least one menu entry with one icon? (Also a disabled entry would be nice)

Looks like the CI is failing in the C++ tests.

   Error: /Users/runner/work/slint/cppbuild/api/cpp/generated_include/slint_builtin_structs_internal.h:139:5: error: unknown type name 'Image'
      Image icon;
      ^

This is because the builtin struct now contain an image. This header is generated in https://github.com/slint-ui/slint/blob/ec1e125e8007e0c3fa086bf354e3e39b1d7a3c1b/api/cpp/cbindgen.rs#L119 , and it should be sufficient to add an #include <slint_image.h> there.

Also the muda implementation in muda.rs is missing.

[ogoffart]

Looking at the PR again, it looks like there are still some issue in the generated headers. Is that something you need help with?

[redstrate]

Looking at the PR again, it looks like there are still some issue in the generated headers. Is that something you need help with?

Absolutely! I have no idea what I'm doing in the C++ part of Slint, so I'm just putting in stuff blind

[ogoffart]

I've fixed the include issue, but there is still an error in C++ 32bit (esp-idf):

 /__w/slint/slint/api/cpp/include/slint_sharedvector.h: In instantiation of 'struct slint::SharedVector<slint::cbindgen_private::MenuEntry>':
/__w/slint/slint/api/cpp/include/slint_window.h:106:31:   required from here
/__w/slint/slint/api/cpp/include/slint_sharedvector.h:227:30: error: static assertion failed: Not yet supported because we would need to add padding
  227 |     static_assert(alignof(T) <= alignof(SharedVectorHeader),
      |                   ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/__w/slint/slint/api/cpp/include/slint_sharedvector.h:227:30: note: the comparison reduces to '(8 <= 4)'

The problem is because Image constains a CacheKey which contains a u64, and so can't be put in a SharedVector because struct for which alignment is bigger than the alignment of the helper data.

https://github.com/slint-ui/slint/blob/a176a553522adb052aa7c50b7e23ef2f9f3ce604/internal/core/graphics/image.rs#L293

Option include:

1. Fix SharedVector to support higher alignment of its data
2. Use a usize instead of a u64 for this field
3. Something else.

Option 2. is the easier, @tronical: do you think it is safe? Otherwise I think Option 1. (fixing SharedVector) should actually be the most correct.

[tronical]

The usize holds a pointer, so u64 is ok for now.

[ogoffart]

(Rebased to fix conflicts)