Adding cpp_info objects model for linking object files

[czoido]

Changelog: Feature: Add objects attribute to the cpp_info so that we can add object files to the linker without having to add those mixed with linker flags.
Docs: conan-io/docs#2243

For the moment it just works with CMakeDeps generator.

It's used like:

def package_info(self):
    self.cpp_info.components.objects = ["myobject.o"]

def package_info(self):
    self.cpp_info.components["say"].objects = ["mycomponent.o"]

Related with:

• [bug] cmake link options treated as files with cmake_find_package generator #8703
• [feature] Support CMake OBJECT libraries #9438
• Handling loose object files #5159
• fix linker flags in cmake (find_package based) generators #8740
• [bug] Regression: PR #8740 breaks adding objects to link through sharedlinkflags #8811

Related info:

• https://cmake.org/cmake/help/latest/prop_tgt/LINK_OPTIONS.html#prop_tgt:LINK_OPTIONS
• https://cmake.org/cmake/help/latest/prop_tgt/INTERFACE_LINK_OPTIONS.html
• https://cmake.org/cmake/help/latest/command/target_link_libraries.html#command:target_link_libraries
• https://cmake.org/cmake/help/latest/prop_tgt/INTERFACE_LINK_LIBRARIES.html
• https://cmake.org/cmake/help/latest/prop_tgt/LINK_LIBRARIES.html
• https://cmake.org/cmake/help/latest/manual/cmake-buildsystem.7.html#object-libraries

[memsharded]

One functional test that really links and execute an app with a couple of objects, for this feature please

[czoido]

One functional test that really links and execute an app with a couple of objects, for this feature please

I'm on it, I already tested the feature with mimalloc: https://github.com/conan-io/conan-center-index/tree/master/recipes/mimalloc

[lasote]

Pretty cool!

[memsharded]

Why the "hello" library? Is not possible to have a package with just the objects? (I would say it is also an expected use case). I guess everything should work, but with CMake, who knows...