Change *.rsi targets to *.expanded.rs #1158
Description
The build system has support for expanding a Rust file path/to/file.rs by way of the .rsi target: make path/to/file.rsi. The extension .rsi comes AFAIK from the C/assembly world and doesn't make much sense for Rust, since it isn't recognized as a Rust file. It also makes it hard to remember how it is named. Thus let's rename the extension to .expanded.rs, that way it's clear what it does and it still has a .rs extension.
This requires submitting a proper patch to the LKML and the Rust for Linux mailing list. Please recall to test your changes (including generating the documentation if changed, running the Rust doctests if changed, etc.), to use a proper title for the commit, to sign your commit under the Developer's Certificate of Origin and to add a Suggested-by: tag, and a Link: tag to this issue. Please see https://docs.kernel.org/process/submitting-patches.html and https://rust-for-linux.com/contributing for details.