Allow CLI to start Zed from local sources

Zed now is able to behave as if it's being started from CLI
(`ZED_FORCE_CLI_MODE` env var)

Zed CLI accepts regular binary file path into `-b` parameter (only *.app before),
and tries to start it as Zed editor with `ZED_FORCE_CLI_MODE` env var
and other params needed.

crates/cli/src/cli.rs

@@ -20,3 +20,7 @@ pub enum CliResponse {
     Stderr { message: String },
     Exit { status: i32 },
 }
+
+/// When Zed started not as an *.app but as a binary (e.g. local development),
+/// there's a possibility to tell it to behave "regularly".
+pub const FORCE_CLI_MODE_ENV_VAR_NAME: &str = "ZED_FORCE_CLI_MODE";