This change moves the lockfile instructions into a script, and instead of removing packages it sets the Conan home directory to a temporary directory.
There are several advantages, such as:
* Not affecting the user's Conan home directory, so there is no need to remove packages.
* Only the script needs to be run, rather than several commands.
This change updates the instructions for how to generate a Conan lockfile that is compatible with Linux, macOS, and Windows.
Whenever Conan dependencies change, the Conan lock file needs to be regenerated. However, different OSes have slightly different requirements, and thus require slightly different dependencies. Luckily a single `conan.lock` file can be used, as long as the union of dependencies is included.
The current instructions in the `BUILD.md` file are insufficient to regenerate the lock file such that it is compatible with all OSes, which this change addresses. The three profiles contain the bare minimum needed to generate the lockfile; it does not particularly matter whether the build type is Debug or Release, for instance.
