[bug] Blocks object not visible / importable

[KerstinKeller]

The documentation suggests, if you want to extend CMakeToolchain with custom blocks, you need to inherit from it.
However, it cannot be imported:

from conan.tools.cmake import CMakeToolchain, CMake, Block

fails with

ImportError: cannot import name 'Block' from 'conan.tools.cmake'

This can be fixed by adding it to the __init__.py (file)[https://github.com/conan-io/conan/blob/1.42.1/conan/tools/cmake/init.py].

Environment Details (include every applicable attribute)

• Conan 1.42.1:

[memsharded]

Yes, this is a bug, unittesting skipped it because of internal import.

For the external interface, probably it deserves a better, specific name, like CMakeToolchainBlock

[memsharded]

Fixed in #10026, will be in 1.43