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/language_settings.rs

@@ -1029,7 +1029,10 @@ fn scroll_debounce_ms() -> u64 {
 #[derive(Debug, Clone, Deserialize, PartialEq, Serialize, JsonSchema)]
 pub struct LanguageTaskConfig {
     /// Extra task variables to set for a particular language.
+    #[serde(default)]
     pub variables: HashMap<String, String>,
+    #[serde(default = "default_true")]
+    pub enabled: bool,
 }
 
 impl InlayHintSettings {