Expose a rust_static_library instead of raw rs file from rust_bindgen

Originally, `rust_bindgen` would originally expose an `action` which
generates a `.rs` file (and sometimes `.c` file if wrap_static_inline
is true). This would move the burden of knowing how to correctly bundle
the generated file on the user where they would have to define a custom
`BINDGEN_RS_FILE` flag which has to be loaded from the code.

In order to eliminate the overhead, the user will treat the
`rust_bindgen` as a `rust_static_library` which can be used by importing
it using `chromium::import` or `use ..` whether it's first-party or not.

The different design also allows the rust toolchain owners to take
finer control on what's being done and what's exposed exactly from
`rust_bindgen` by tweaking the `bindings.rs` file.

This also fixes Cronet in AOSP where Soong (AOSP build system) does not
allow a target to access another target's output through its path which
what most clients of `rust_bindgen` did through the custom rustflag.

In order to stay backward compatible with older consumers of
`rust_bindgen`, we created `rust_bindgen_generator` which generates the
raw rust which allows flexibility in usage.

Bug: 373864033
Change-Id: I3d72aa8ecd11151235d3dd387b313c9d0309d4a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5953710
Auto-Submit: Mohannad Farrag <aymanm@google.com>
Commit-Queue: David Benjamin <davidben@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1374672}


CrOS-Libchrome-Original-Commit: 63ce6fc17e6c065cc492e6e6b740f8a1e4322181

Author: aymanm-google

base/logging/rust_logger.rs

@@ -6,12 +6,12 @@ use log::Level::{Debug, Error, Info, Trace, Warn};
 use log::{LevelFilter, Metadata, Record};
 use std::ffi::CString;
 
-mod rust_log_integration {
-    include!(env!("RUST_LOG_INTEGRATION_BINDGEN_RS_FILE"));
+chromium::import! {
+    "//base:rust_log_bindgen";
 }
 
-use rust_log_integration::root::logging::internal::print_rust_log;
-use rust_log_integration::root::logging::internal::{
+use rust_log_bindgen::logging::internal::print_rust_log;
+use rust_log_bindgen::logging::internal::{
     RustLogSeverity_DEBUG, RustLogSeverity_ERROR, RustLogSeverity_INFO, RustLogSeverity_TRACE,
     RustLogSeverity_WARNING,
 };