Add GitHub Composite Action to install CMake on macOS runners

Author: maddyadams

.github/actions/build-swiftusd/action.yml

@@ -29,6 +29,9 @@ inputs:
 runs:
   using: "composite"
   steps:
+
+  - name: Install CMake
+    uses: ./.github/actions/install-cmake
 
   - name: Clone OpenUSD
     uses: actions/checkout@v5

.github/actions/install-cmake/action.yml

@@ -0,0 +1,67 @@
+#===----------------------------------------------------------------------===#
+# This source file is part of github.com/apple/SwiftUsd
+#
+# Copyright © 2025 Apple Inc. and the SwiftUsd project authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#  https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#===----------------------------------------------------------------------===#
+
+# Installs CMake 3.26.5 for macOS
+
+name: Install CMake
+
+runs:
+  using: "composite"
+  steps:
+
+  - name: Download CMake
+    run: |
+      curl https://github.com/Kitware/CMake/releases/download/v3.26.5/cmake-3.26.5-macos-universal.dmg \
+        --output CMake.dmg
+    working-directory: ${{ runner.temp }}
+    shell: bash
+    
+
+  - name: Verify SHA256 checksum
+    run: |
+      # Hard-coded checksum taken from https://github.com/Kitware/CMake/releases/download/v3.26.5/cmake-3.26.5-SHA-256.txt,
+      # cmake-3.26.5-macos-universal.dmg
+      echo '18fb759bbdd04309be6a8e12920a8183ebbb17b331a6b7fc6a4071a68e5c81fd *CMake.dmg' | shasum -a 256 -c
+    working-directory: ${{ runner.temp }}
+    shell: bash
+    
+
+  - name: Attach DMG
+    run: hdiutil attach CMake.dmg
+    working-directory: ${{ runner.temp }}
+    shell: bash
+
+  - name: Copy app to permanent location
+    run: |
+      cp /Volumes/CMake/CMake.app ../CMake.app
+      hdiutil detach /Volumes/CMake
+    working-directory: ${{ github.workspace }
+    shell: bash
+      
+  - name: Add CMake to PATH
+    run: |
+      # Note: `export PATH=` doesn't work for GitHub actions, the environment variable
+      # must be set by redirecting into GITHUB_ENV
+      echo "PATH=$PATH:$GITHUB_WORKSPACE/../CMake.app/Contents/bin" >> $GITHUB_ENV
+    shell: bash
+
+  - name: Test CMake is in PATH
+    run: which cmake
+    shell: bash