task: Add task contexts (#8675)

This PR supplements tasks with additional environment variables; ideally
we'll be able to write a task like:
`cargo test -p $ZED_CURRENT_PACKAGE -- $ZED_CURRENT_FUNCTION`
- [x] Flesh out multibuffer interactions
- [x] Add ZED_SYMBOL detection based on tree-sitter queries
- [ ] Add release note and demo
- [x] Figure out a solution for rerun dilemma - should `task: rerun`
reevaluate contexts for tasks?

This PR introduced the following variables:
- ZED_COLUMN - current line column
- ZED_ROW - current line row
and the following, which are available for buffers with associated
files:
- ZED_WORKTREE_ROOT - absolute path to the root of the current worktree.
- ZED_FILE - absolute path to the file
- ZED_SYMBOL - currently selected symbol; should match the last symbol
shown in a symbol breadcrumb (e.g. `mod tests > fn test_task_contexts`
should be equal to ZED_SYMBOL of `test_task_contexts`). Note that this
isn't necessarily a test function or a function at all.

Also, you can use them in `cwd` field of definitions (note though that
we're using https://docs.rs/subst/latest/subst/#features for that, so
don't expect a full shell functionality to work); the syntax should
match up with your typical Unix shell.


Release Notes:

- Added task contexts, which are additional environment variables set by
Zed for task execution; task content is dependent on the state of the
editor at the time the task is spawned.

---------

Co-authored-by: Anthony <anthonyeid7@protonmail.com>

crates/task/src/lib.rs

@@ -36,6 +36,15 @@ pub struct SpawnInTerminal {
     pub allow_concurrent_runs: bool,
 }
 
+/// Keeps track of the file associated with a task and context of tasks execution (i.e. current file or current function)
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
+pub struct TaskContext {
+    /// A path to a directory in which the task should be executed.
+    pub cwd: Option<PathBuf>,
+    /// Additional environment variables associated with a given task.
+    pub env: HashMap<String, String>,
+}
+
 /// Represents a short lived recipe of a task, whose main purpose
 /// is to get spawned.
 pub trait Task {
@@ -44,10 +53,10 @@ pub trait Task {
     /// Human readable name of the task to display in the UI.
     fn name(&self) -> &str;
     /// Task's current working directory. If `None`, current project's root will be used.
-    fn cwd(&self) -> Option<&Path>;
+    fn cwd(&self) -> Option<&str>;
     /// Sets up everything needed to spawn the task in the given directory (`cwd`).
     /// If a task is intended to be spawned in the terminal, it should return the corresponding struct filled with the data necessary.
-    fn exec(&self, cwd: Option<PathBuf>) -> Option<SpawnInTerminal>;
+    fn exec(&self, cx: TaskContext) -> Option<SpawnInTerminal>;
 }
 
 /// [`Source`] produces tasks that can be scheduled.