Honor build.target-dir from .cargo/config.toml

[laundmo]

This is a follow-up to:

• cargo.targetDir seems to ignore $CARGO_TARGET_DIR #18296
• minor: Honor CARGO_TARGET_DIR for cargo target dir config #18827

With that PR, rust-analyzer honors the environment variable CARGO_TARGET_DIR but this is not the only location users may change the target directory.

The other option is using target-dir in the Cargo config:
https://doc.rust-lang.org/cargo/reference/config.html#buildtarget-dir
Which rust-analyzer still doesn't honor.

Due to the same reasoning it was decided R-A should honor CARGO_TARGET_DIR, i would request that this config be honored as well.