Move GitHub Actions CI scripts into separate files

Break the workflow into smaller stages (Configure, Build, Install,
Package, etc.) so that you can see exactly which stage failed in the
GitHub Actions run log.

Create a separate Bash CI script for each job stage (configure.sh,
build.sh, install.sh, package.sh, etc.) to reduce the size of the main
YAML workflow file and enable Bash syntax highlighting.

Close #917

scripts/ci/dependencies.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+
+((${BASH_VERSION%%.*} >= 4)) || echo >&2 "$0: Warning: Using ancient Bash version ${BASH_VERSION}."
+
+set -euxo pipefail
+
+if [[ "${OSTYPE}" == msys* ]]; then # Windows
+
+    # Python packages
+    pip_packages=(
+        conan
+    )
+    pip3 install "${pip_packages[@]}"
+
+elif [[ "${OSTYPE}" == darwin* ]]; then # macOS
+
+    # Homebrew packages
+    brew_packages=(
+        bash # macOS ships with Bash v3 for licensing reasons so upgrade it now
+        conan
+    )
+    brew install "${brew_packages[@]}"
+
+else # Linux & others
+
+    # Distribution packages
+    if which apt-get; then
+        apt_packages=(
+            libasound2-dev
+            libgtk2.0-dev
+            gettext
+            python3-pip
+        )
+        sudo apt-get update -y
+        sudo apt-get install -y --no-install-recommends "${apt_packages[@]}"
+        sudo apt-get remove -y ccache
+    else
+        echo >&2 "$0: Error: You don't have a recognized package manager installed."
+        exit 1
+    fi
+
+    # Python packages
+    pip_packages=(
+        conan
+    )
+    pip3 install wheel setuptools # need these first to install other packages (e.g. conan)
+    pip3 install "${pip_packages[@]}"
+
+fi