Support tasks from rust-analyzer (#28359)

(and any other LSP server in theory, if it exposes any LSP-ext endpoint
for the same)

Closes https://github.com/zed-industries/zed/issues/16160

* adds a way to disable tree-sitter tasks (the ones from the plugins,
enabled by default) with
```json5
"languages": {
  "Rust": "tasks": {
      "enabled": false
    }
  }
}
```
language settings

* adds a way to disable LSP tasks (the ones from the rust-analyzer
language server, enabled by default) with
```json5
"lsp": {
  "rust-analyzer": {
    "enable_lsp_tasks": false,
  }
}
```

* adds rust-analyzer tasks into tasks modal and gutter:

<img width="1728" alt="modal"
src="https://github.com/user-attachments/assets/22b9cee1-4ffb-4c9e-b1f1-d01e80e72508"
/>

<img width="396" alt="gutter"
src="https://github.com/user-attachments/assets/bd818079-e247-4332-bdb5-1b7cb1cce768"
/>


Release Notes:

- Added tasks from rust-analyzer

crates/language/src/task_context.rs

@@ -5,6 +5,7 @@ use crate::{LanguageToolchainStore, Location, Runnable};
 use anyhow::Result;
 use collections::HashMap;
 use gpui::{App, Task};
+use lsp::LanguageServerName;
 use task::{TaskTemplates, TaskVariables};
 use text::BufferId;
 
@@ -15,6 +16,7 @@ pub struct RunnableRange {
     pub runnable: Runnable,
     pub extra_captures: HashMap<String, String>,
 }
+
 /// Language Contexts are used by Zed tasks to extract information about the source file where the tasks are supposed to be scheduled from.
 /// Multiple context providers may be used together: by default, Zed provides a base [`BasicContextProvider`] context that fills all non-custom [`VariableName`] variants.
 ///
@@ -40,4 +42,9 @@ pub trait ContextProvider: Send + Sync {
     ) -> Option<TaskTemplates> {
         None
     }
+
+    /// A language server name, that can return tasks using LSP (ext) for this language.
+    fn lsp_task_source(&self) -> Option<LanguageServerName> {
+        None
+    }
 }