Feature request: Support using target from .cargo/config.toml

[rlabrecque]

I'm not sure if this specific config file is used at all by rust-analyzer (it seems poorly documented), but I have my project set up well for everything else and rust-analyzer was still wanting to use my default target/toolchain, rather than the project specified one.

In the meantime I needed to add a settings.json to my project folder with the following, which works well, but it would just be nicer if the target was automatically picked up from .cargo/config.toml:

{
	/*"rust-analyzer.linkedProjects": [
		{
			"crates": [
				{
					"root_module": "a/src/main.rs",
					"edition": "2018",
					"deps": [],
					"target": "i686-pc-windows-msvc",
				},
				{
					"root_module": "b/src/lib.rs",
					"edition": "2018",
					"deps": [],
					"target": "i686-pc-windows-msvc",
				},
				{
					"root_module": "c/src/lib.rs",
					"edition": "2018",
					"deps": [],
					"target": "i686-pc-windows-msvc",
				},
			]
		}
	],*/
	"rust-analyzer.cargo.target": "i686-pc-windows-msvc",
}

Thanks!