Rename bitcode-in-rlib option to embed-bitcode

This commit finishes work first pioneered in #70458 and started in #71528.
The `-C bitcode-in-rlib` option, which has not yet reached stable, is
renamed to `-C embed-bitcode` since that more accurately reflects what
it does now anyway. Various tests and such are updated along the way as
well.

This'll also need to be backported to the beta channel to ensure we
don't accidentally stabilize `-Cbitcode-in-rlib` as well.

src/test/ui/lto-and-no-bitcode-in-rlib.rs

@@ -1,3 +1,3 @@
-// compile-flags: -C lto -C bitcode-in-rlib=no
+// compile-flags: -C lto -C embed-bitcode=no
 
 fn main() {}

src/test/ui/lto-and-no-bitcode-in-rlib.stderr

@@ -1,2 +1,2 @@
-error: options `-C bitcode-in-rlib=no` and `-C lto` are incompatible
+error: options `-C embed-bitcode=no` and `-C lto` are incompatible