Docs: Update developing zed docs to match (#21379)

Some changes just so the build docs for the different os matches each
other :)

macos:
- moved `rust wasm toolchain install` up under `rust install` (match
windows docs)
- add instructions to update rust if already installed (match windows
and linux docs)

windows:
- add `(required by a dependency)` to cmake install (match macos docs)

Release Notes:

- N/A

docs/src/development/linux.md

@@ -6,11 +6,7 @@ Clone down the [Zed repository](https://github.com/zed-industries/zed).
 
 ## Dependencies
 
-- Install [Rust](https://www.rust-lang.org/tools/install). If it's already installed, make sure it's up-to-date:
-
-  ```sh
-  rustup update
-  ```
+- Install [rustup](https://www.rust-lang.org/tools/install)
 
 - Install the necessary system libraries:
 

docs/src/development/macos.md

@@ -6,7 +6,8 @@ Clone down the [Zed repository](https://github.com/zed-industries/zed).
 
 ## Dependencies
 
-- Install [Rust](https://www.rust-lang.org/tools/install)
+- Install [rustup](https://www.rust-lang.org/tools/install)
+
 - Install [Xcode](https://apps.apple.com/us/app/xcode/id497799835?mt=12) from the macOS App Store, or from the [Apple Developer](https://developer.apple.com/download/all/) website. Note this requires a developer account.
 
 > Ensure you launch Xcode after installing, and install the macOS components, which is the default option.
@@ -24,12 +25,6 @@ Clone down the [Zed repository](https://github.com/zed-industries/zed).
   sudo xcodebuild -license accept
   ```
 
-- Install the Rust wasm toolchain:
-
-  ```sh
-  rustup target add wasm32-wasip1
-  ```
-
 - Install `cmake` (required by [a dependency](https://docs.rs/wasmtime-c-api-impl/latest/wasmtime_c_api/))
 
   ```sh

docs/src/development/windows.md

@@ -8,21 +8,11 @@ Clone down the [Zed repository](https://github.com/zed-industries/zed).
 
 ## Dependencies
 
-- Install [Rust](https://www.rust-lang.org/tools/install). If it's already installed, make sure it's up-to-date:
-
-  ```sh
-  rustup update
-  ```
-
-- Install the Rust wasm toolchain:
-
-  ```sh
-  rustup target add wasm32-wasip1
-  ```
+- Install [rustup](https://www.rust-lang.org/tools/install)
 
 - Install [Visual Studio](https://visualstudio.microsoft.com/downloads/) with the optional components `MSVC v*** - VS YYYY C++ x64/x86 build tools` and `MSVC v*** - VS YYYY C++ x64/x86 Spectre-mitigated libs (latest)` (`v***` is your VS version and `YYYY` is year when your VS was released. Pay attention to the architecture and change it to yours if needed.)
 - Install Windows 11 or 10 SDK depending on your system, but ensure that at least `Windows 10 SDK version 2104 (10.0.20348.0)` is installed on your machine. You can download it from the [Windows SDK Archive](https://developer.microsoft.com/windows/downloads/windows-sdk/)
-- Install [CMake](https://cmake.org/download)
+- Install [CMake](https://cmake.org/download) (required by [a dependency](https://docs.rs/wasmtime-c-api-impl/latest/wasmtime_c_api/))
 
 ## Backend dependencies