[feat] Take into account 'requires' information to propagate only those components

[jgsogo]

Changelog: Feature: Allow packages that do not declare components to depend on other packages components and manage transitivity correctly, with the new self.cpp_info.requires attribute.
Docs: conan-io/docs#1864

On top of #7641
Closes #7475

This PR introduces a new feature. Generators cmake_find_package[_multi] and pkg_config (those that implement components) will take into account the requirements and components listed in the requires field and will use only those targets when adding dependencies to the consumers.

Example 1

class Recipe:
    names = "middle"
    requires = "top/version"

    def package_info(self):
        self.cpp_info.components["middle1"].requires = ["top::cmp1"]

will generate this equivalent CMake lines:

add_library(middle::middle INTERFACE IMPORTED)
find_dependency(top)
set_property(TARGET middle::middle PROPERTY INTERFACE_LINK_LIBRARIES top::cmp1)

before it was using top::top

Example 2

As we don't want to force every recipe to use components in order to take advantage of this feature, there is a new cpp_info.requires property that offers the same capabilities as the one defined in the components:

class Recipe:
    names = "middle"
    requires = "top/version"

    def package_info(self):
        self.cpp_info.requires = ["top::cmp1"]

will generate this equivalent CMake lines:

add_library(middle::middle INTERFACE IMPORTED)
find_dependency(top)
set_property(TARGET middle::middle PROPERTY INTERFACE_LINK_LIBRARIES top::cmp1)

[memsharded]

Is the test so slow that a setUpClass would make sense? Why not a setUp and make sure there are no cross-effects between tests?

[jgsogo]

It was cleaner IMO, the test_xxx contains only the statements that are interesting to the test itself, while the setup is guaranteed to be the same for all of them. When a new generator implements this feature I hope we write a new test_xxxx function for it using the same recipes, this way it is harder to write something custom for that generator.

But I can move it to setUp or even copy it to every single test, we don't have anything written about this.

[jgsogo]

I'm moving it to a setUp method