Summary

Taking over #17427 from @shs96c who was unable to complete it.

This PR enables cross-compilation of selenium-manager from any host platform to all target platforms (Linux x86_64/aarch64, macOS aarch64, Windows x86_64/aarch64) using the hermetic LLVM toolchain.

Key changes (from Simon's original work)

• Upgrades rules_rs 0.0.61 → 0.0.76 and llvm 0.7.9 → 0.8.0
• Registers LLVM exec toolchains for Linux (x86_64, aarch64) and macOS (aarch64)
• Adds cross-compile targets for all five platforms in rust/BUILD.bazel
• Restructures language binding (py, rb, dotnet, java) BUILD files to consume a per-arch bundle
• On Windows, uses native MSVC build for the host arch and stubs the rest (cross-compile from Linux for releases)
• Adds musl targets for Linux (no glibc dependency) and gnullvm targets for Windows

Fixes applied in this PR (on top of Simon's work)

• windows-link/windows-targets patches: The original patches changed include_str!("../readme.md") → include_str!("../README.md") but the crate only ships readme.md and Bazel's Rust sandbox doesn't include non-source files anyway. Fixed by removing the doc attribute entirely.
• Windows MSVC linker: The hermetic LLVM package for Windows provides only a GNU-mode clang++.exe which can't handle MSVC-style linker flags (/NOLOGO, .lib files). Re-enabled MSVC CC auto-detection on Windows so Visual Studio's link.exe is used for MSVC targets.

Known remaining issues

• macOS Rust tests: aws-lc-sys (pulled in transitively through reqwest → rustls → rustls-platform-verifier) requires CoreServices.framework which is not in the hermetic LLVM macOS SDK sysroot. Adding the aarch64 macOS exec LLVM toolchain (new in this PR) causes this to surface. Fixing requires either a different TLS cert backend or a richer macOS sysroot — tracked as a follow-up.

Closes #17427