Meta: Rebuild Rust crates when the toolchain changes, not just sources

Problem: After a git pull of master, builds fail with an error message
about multiple/duplicate rust_eh_personality definitions/symbols.

Cause: LibWeb links two Rust staticlibs: libweb_content_blocker_rust and
libweb_rust. Both bundle Rust’s standard library (std). When we re-pin
rust-toolchain.toml, a git pull moves a rustup user’s compiler — but we
were only rebuilding the crate whose .rs also changed. So that left one
crate on the old std, and the other crate on the new std.

Fix: Make the cargo custom commands also depend on rust-toolchain.toml
and rustc — so a toolchain change re-triggers every Rust crate.

Fixes https://github.com/LadybirdBrowser/ladybird/issues/9854
Fixes https://github.com/LadybirdBrowser/ladybird/issues/9643

Meta/CMake/rust_crate.cmake

@@ -54,6 +54,7 @@ function(import_rust_crate)
                 -P "${CMAKE_CURRENT_FUNCTION_LIST_DIR}/sync_rust_ffi_header.cmake"
         DEPENDS "${manifest_path}"
             "${workspace_dir}/Cargo.lock" "${workspace_dir}/Cargo.toml"
+            "${RUST_RUSTC}" "${CMAKE_SOURCE_DIR}/rust-toolchain.toml"
         DEPFILE "${depfile}"
         COMMENT "Building Rust crate ${ARG_CRATE_NAME}"
         USES_TERMINAL
@@ -108,6 +109,7 @@ function(build_rust_binary)
         COMMAND ${CMAKE_COMMAND} -E copy_if_different "${cargo_binary}" "${output_binary}"
         DEPENDS "${manifest_path}"
             "${workspace_dir}/Cargo.lock" "${workspace_dir}/Cargo.toml"
+            "${RUST_RUSTC}" "${CMAKE_SOURCE_DIR}/rust-toolchain.toml"
         DEPFILE "${depfile}"
         COMMENT "Building Rust binary ${ARG_BINARY_NAME}"
         USES_TERMINAL