Add language server for Terraform (#7657)

* Depends on: https://github.com/zed-industries/zed/pull/7449
* Closes: https://github.com/zed-industries/zed/issues/5098

---

This PR adds support for downloading and running the Terraform language
server for `*.tf` and `*.tfvars` files. I've verified that the code
works for `aarch64` and `x86_64` macOS. Downloading new language server
versions on release also works as expected.

Furthermore this PR adds:
- A short docs page for Terraform
- An icon for `*.tf` and `*.tfvars` files

## UX

### File Icons

![CleanShot 2024-02-10 at 23 10
13@2x](https://github.com/zed-industries/zed/assets/45985/6f7cd4f0-e94c-4cfb-b3e9-64b0e33c8a43)

### Completion

![CleanShot 2024-02-13 at 20 54
15@2x](https://github.com/zed-industries/zed/assets/45985/18fafa3b-cb50-4f51-b071-ca9eee3521a6)

### Hover

![CleanShot 2024-02-13 at 20 53
40@2x](https://github.com/zed-industries/zed/assets/45985/4d215315-e019-4d3d-b23c-2691db1803e3)

### Go to definition

![2024-02-13 20 56
28](https://github.com/zed-industries/zed/assets/45985/c21d562f-eb0b-4df9-9175-c53b9923344e)

### Formatting

![2024-02-13 20 59
06](https://github.com/zed-industries/zed/assets/45985/0cdf4ec5-e231-4c8a-a257-cae30a8edc8b)

and more!

## Known issue(s)

@fdionisi discovered that sometimes completion results are inserted with
the wrong indentation. Or rather, if you look closely, they are inserted
with the correct indentation and then something shifts the closing `}`.
I don't think this is related to LSP support and can be addressed in a
separate PR.

![2024-02-13 20 58
16](https://github.com/zed-industries/zed/assets/45985/94a118dd-95f5-4e38-8f83-75fec7a0dddf)

Release Notes:

- Add language server support for Terraform
([#5098](https://github.com/zed-industries/zed/issues/5098)).

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

assets/icons/file_icons/file_types.json

@@ -133,6 +133,8 @@
     "svelte": "template",
     "svg": "image",
     "swift": "swift",
+    "tf": "terraform",
+    "tfvars": "terraform",
     "tiff": "image",
     "toml": "toml",
     "ts": "typescript",
@@ -280,6 +282,9 @@
     "template": {
       "icon": "icons/file_icons/html.svg"
     },
+    "terraform": {
+      "icon": "icons/file_icons/terraform.svg"
+    },
     "terminal": {
       "icon": "icons/file_icons/terminal.svg"
     },

assets/icons/file_icons/terraform.svg

@@ -0,0 +1,6 @@
+<svg width="32" height="32" viewBox="0 0 32 32" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path fill-rule="evenodd" clip-rule="evenodd" d="M12.5066 8.01531L19.2375 12.1073V20.2894L12.5066 16.1992V8.01531Z" fill="black"/>
+<path fill-rule="evenodd" clip-rule="evenodd" d="M20.0294 12.1073V20.2894L27.1563 16.1992V8.01531L20.0294 12.1073Z" fill="black"/>
+<path fill-rule="evenodd" clip-rule="evenodd" d="M4.58781 3.66V11.5787L11.7147 15.5381V7.61937L4.58781 3.66Z" fill="black"/>
+<path fill-rule="evenodd" clip-rule="evenodd" d="M12.5066 25.04L19.2375 29V21.1348V21.0818L12.5066 17.1219V25.04Z" fill="black"/>
+</svg>