docs: Improve Elixir HEEX language server documentation (#38363)

Closes: https://github.com/zed-industries/zed/issues/38009

Release Notes:

- N/A

docs/src/languages/elixir.md

@@ -22,19 +22,14 @@ The Elixir extension offers language server support for `expert`, `elixir-ls`, `
 To switch to `expert`, add the following to your `settings.json`:
 
 ```json
-{
   "languages": {
     "Elixir": {
-      "language_servers": [
-        "expert",
-        "!elixir-ls",
-        "!next-ls",
-        "!lexical",
-        "..."
-      ]
+      "language_servers": ["expert", "!elixir-ls", "!next-ls", "!lexical", "..."]
+    },
+    "HEEX": {
+      "language_servers": ["expert", "!elixir-ls", "!next-ls", "!lexical", "..."]
     }
   }
-}
 ```
 
 ### Next LS
@@ -42,19 +37,14 @@ To switch to `expert`, add the following to your `settings.json`:
 To switch to `next-ls`, add the following to your `settings.json`:
 
 ```json
-{
   "languages": {
     "Elixir": {
-      "language_servers": [
-        "next-ls",
-        "!expert",
-        "!elixir-ls",
-        "!lexical",
-        "..."
-      ]
+      "language_servers": ["next-ls", "!expert", "!elixir-ls", "!lexical", "..."]
+    },
+    "HEEX": {
+      "language_servers": ["next-ls", "!expert", "!elixir-ls", "!lexical", "..."]
     }
   }
-}
 ```
 
 ### Lexical
@@ -62,19 +52,14 @@ To switch to `next-ls`, add the following to your `settings.json`:
 To switch to `lexical`, add the following to your `settings.json`:
 
 ```json
-{
   "languages": {
     "Elixir": {
-      "language_servers": [
-        "lexical",
-        "!expert",
-        "!elixir-ls",
-        "!next-ls",
-        "..."
-      ]
+      "language_servers": ["lexical", "!expert", "!elixir-ls", "!next-ls", "..."]
+    },
+    "HEEX": {
+      "language_servers": ["lexical", "!expert", "!elixir-ls", "!next-ls", "..."]
     }
   }
-}
 ```
 
 ## Setting up `elixir-ls`
@@ -121,13 +106,13 @@ You can pass additional elixir-ls workspace configuration options via lsp settin
 The following example disables dialyzer:
 
 ```json
-"lsp": {
-  "elixir-ls": {
-    "settings": {
-      "dialyzerEnabled": false
+  "lsp": {
+    "elixir-ls": {
+      "settings": {
+        "dialyzerEnabled": false
+      }
     }
   }
-}
 ```
 
 See [ElixirLS configuration settings](https://github.com/elixir-lsp/elixir-ls#elixirls-configuration-settings) for more options.