Implement basic support for VS Code debug configurations (#29160)

- [x] Basic implementation
- [x] Match common VSC debug extension names to Zed debug adapters
- [ ] ~~`preLaunchTask` support~~ descoped for this PR

Release Notes:

- N/A

crates/task/src/lib.rs

@@ -4,6 +4,7 @@ mod debug_format;
 mod serde_helpers;
 pub mod static_source;
 mod task_template;
+mod vscode_debug_format;
 mod vscode_format;
 
 use collections::{HashMap, HashSet, hash_map};
@@ -22,6 +23,7 @@ pub use task_template::{
     DebugArgs, DebugArgsRequest, HideStrategy, RevealStrategy, TaskModal, TaskTemplate,
     TaskTemplates, TaskType,
 };
+pub use vscode_debug_format::VsCodeDebugTaskFile;
 pub use vscode_format::VsCodeTaskFile;
 pub use zed_actions::RevealTarget;
 
@@ -522,3 +524,50 @@ impl ShellBuilder {
         }
     }
 }
+
+type VsCodeEnvVariable = String;
+type ZedEnvVariable = String;
+
+struct EnvVariableReplacer {
+    variables: HashMap<VsCodeEnvVariable, ZedEnvVariable>,
+}
+
+impl EnvVariableReplacer {
+    fn new(variables: HashMap<VsCodeEnvVariable, ZedEnvVariable>) -> Self {
+        Self { variables }
+    }
+    // Replaces occurrences of VsCode-specific environment variables with Zed equivalents.
+    fn replace(&self, input: &str) -> String {
+        shellexpand::env_with_context_no_errors(&input, |var: &str| {
+            // Colons denote a default value in case the variable is not set. We want to preserve that default, as otherwise shellexpand will substitute it for us.
+            let colon_position = var.find(':').unwrap_or(var.len());
+            let (left, right) = var.split_at(colon_position);
+            if left == "env" && !right.is_empty() {
+                let variable_name = &right[1..];
+                return Some(format!("${{{variable_name}}}"));
+            }
+            let (variable_name, default) = (left, right);
+            let append_previous_default = |ret: &mut String| {
+                if !default.is_empty() {
+                    ret.push_str(default);
+                }
+            };
+            if let Some(substitution) = self.variables.get(variable_name) {
+                // Got a VSCode->Zed hit, perform a substitution
+                let mut name = format!("${{{substitution}");
+                append_previous_default(&mut name);
+                name.push('}');
+                return Some(name);
+            }
+            // This is an unknown variable.
+            // We should not error out, as they may come from user environment (e.g. $PATH). That means that the variable substitution might not be perfect.
+            // If there's a default, we need to return the string verbatim as otherwise shellexpand will apply that default for us.
+            if !default.is_empty() {
+                return Some(format!("${{{var}}}"));
+            }
+            // Else we can just return None and that variable will be left as is.
+            None
+        })
+        .into_owned()
+    }
+}