Fix filename in FindPackageHandleStandardArgs for cmake_find_package generator

[danimtb]

Changelog: Bugfix: Fix cpp_info filename in FindPackageHandleStandardArgs for cmake_find_package generator.
Docs: omit

#tags: slow

• Refer to the issue that supports this Pull Request: closes [bug] CMake compontent 'filename' produces error in generated find.cmake and causes conflicts when consumer packages #7574
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

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[uilianries]

This PR should solve Protobuf names: https://cmake.org/cmake/help/v3.9/module/FindProtobuf.html 💯

[jgsogo]

I see _VERSION, at least for Protobuf, follows the filename and not the namespace. With this change it would still be protobuf_VERSION instead of Protobuf_VERSION, right?

[danimtb]

@jgsogo I did not think about this issue but I think it will be useful to have that change as well

[jgsogo]

I think that the orthodox way is to use the filename for all these variables involved in the FindPackageHandleStandardArgs. Again, I'm sure there are exceptions out there 😢 , but I really think those exceptions should be handle by some build-module, we cannot add more items to cpp_info just because CMake 🥊