When loading workspaces fails, tell the user if the linkedProjects config is set

[Veykril]

Currently when someone has the linkedProjects config set and their workspace fails to load (due to the config pointing to non-existing paths or similar), the user will just get confused as r-a doesn't tell them anything else. We should tell them loud and clear that it is most likely a misconfiguration of the linkedProjects config causing them problems.

[stupendoussuperpowers]

could you clarify what you expect the error message to be/what you see currently?

for me, I see the following when it fails to load a linkedProject from the settings, which does point to a failure and a suggestion with it -

[ERROR rust_analyzer::config] failed to load linked project: project root must point to Cargo.toml or rust-project.json: /home/../../.\Cargo.toml

[Veykril]

Relevant part to check is here

rust-analyzer/crates/rust-analyzer/src/reload.rs

Lines 175 to 178 in 8a23314

	if let Err(_) = self.fetch_workspace_error() {
	status.health = lsp_ext::Health::Error;
	message.push_str("Failed to load workspaces.\n\n");
	}

We should check whether the linkedProjects config is set, and if yes add a note to that message that the user should check whether those projects are valid/exist.

[stupendoussuperpowers]

will submit a pull request for this.