(maint) Refactor testing GitHub Actions

Previously the CI testing used Azure DevOps pipelines with hosted agents. This
commit:
* Changes the build and test process to not be destructive and instead create
 the moudle in the 'Output' directory
* Adds the ability the use a different directory to load the module from before
 running the Pester tests
* Uploads the Test Results and Code Coverage as per AzDo pipelines
* Installs PowerShell on the test agent when needed.  Mainly needed to x86
 version of PowerShell 7
* Updates the module testing to use relative path to the module root instead of
 assuming the path is in a fixed location

.github/workflows/ci.yaml

@@ -0,0 +1,99 @@
+name: BurntToast CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  Win2019-x64-pwsh:
+    name: Server 2019 - PowerShell - x64
+    runs-on: windows-2019
+    steps:
+      - uses: actions/checkout@v2
+      - name: Perform a Pester test from the command-line
+        shell: pwsh
+        run: ./Tasks/build.ps1 -Bootstrap -Test
+
+  Win2019-x86-pwsh:
+    name: Server 2019 - PowerShell - x86
+    runs-on: windows-2019
+    steps:
+      - uses: actions/checkout@v2
+      - name: Perform a Pester test from the command-line
+        shell: pwsh
+        run: |
+          $Pwsh32 = .github/workflows/pwsh32.ps1
+          & $Pwsh32 -File ./Tasks/build.ps1 -Bootstrap -Test
+
+  Win2019-x64-winpwsh:
+    name: Server 2019 - Windows PowerShell - x64
+    runs-on: windows-2019
+    steps:
+      - uses: actions/checkout@v2
+      - name: Perform a Pester test from the command-line
+        shell: powershell
+        run: ./Tasks/build.ps1 -Bootstrap -Test
+
+  Win2019-x86-winpwsh:
+    name: Server 2019 - Windows PowerShell - x86
+    runs-on: windows-2019
+    steps:
+      - uses: actions/checkout@v2
+      - name: Perform a Pester test from the command-line
+        shell: powershell
+        # TODO: This could be problematic with hardcoding
+        run: C:\Windows\syswow64\WindowsPowerShell\v1.0\powershell.exe -File ./Tasks/build.ps1 -Bootstrap -Test
+
+  build-and-oat-module:
+    name: Build Module and OAT
+    needs: ["Win2019-x64-pwsh", "Win2019-x64-winpwsh", "Win2019-x86-pwsh", "Win2019-x86-winpwsh"]
+    runs-on: windows-2019
+    steps:
+      - uses: actions/checkout@v2
+      - name: Compile Module
+        shell: pwsh
+        run: ./Tasks/build.ps1 -Bootstrap -Compile
+      - name: OAT
+        shell: pwsh
+        env:
+          # Use the compiled module for testing
+          BURNTTOAST_MODULE_ROOT: './Output/BurntToast/BurntToast.psd1'
+        run: |
+          ./Tasks/build.ps1 -Test -CodeCoverage
+      - name: Upload Test Results
+        if: always()
+        uses: actions/upload-artifact@v2
+        with:
+          name: test-results
+          path: "*.xml"
+      - name: Upload PowerShell Module
+        if: always()
+        uses: actions/upload-artifact@v2
+        with:
+          name: burnttoast-module
+          path: "./Output/BurntToast/"
+
+  publish-test-results:
+    name: "Publish Tests Results"
+    needs: build-and-oat-module
+    runs-on: ubuntu-latest
+    if: always()
+    steps:
+      - name: Download Artifacts
+        uses: actions/download-artifact@v2
+        with:
+          name: test-results
+          path: artifacts
+      - name: Publish Unit Test Results
+        uses: EnricoMi/publish-unit-test-result-action@v1
+        with:
+          files: artifacts/**/TestResults.xml
+      - uses: codecov/codecov-action@v2
+        if: always()
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          files: artifacts/CoverageResults.xml

.github/workflows/pwsh32.ps1

@@ -0,0 +1,25 @@
+param(
+    [Switch]$Force
+)
+$CurrentPSVersion = "$($PSVersionTable.PSVersion.Major).$($PSVersionTable.PSVersion.Minor).$($PSVersionTable.PSVersion.Patch)"
+
+$DownloadDir = Join-Path $PSScriptRoot '../../downloads'
+If (-Not(Test-Path $DownloadDir)) { New-Item -Path $DownloadDir -ItemType 'Directory' | Out-Null }
+
+$PwshZip = Join-Path $DownloadDir 'pwsh.zip'
+If ((Test-Path $PwshZip) -and $Force) { Remove-Item -Path $DownloadDir -Force -Confirm:$false | Out-Null }
+If (-Not (Test-Path $PwshZip)) {
+    $DownloadUrl = "https://github.com/PowerShell/PowerShell/releases/download/v$CurrentPSVersion/PowerShell-$CurrentPSVersion-win-x86.zip"
+    Write-Host "Downloading $DownloadURL ..."
+    Invoke-WebRequest -Uri $DownloadUrl -OutFile $PwshZip
+} else {
+    Write-Host "ZIP file has been downloaded"
+}
+
+$PwshExtract = Join-Path $DownloadDir 'pwsh32'
+If ((Test-Path $PwshExtract) -and $Force) { Remove-Item -Path $PwshExtract -Force -Confirm:$false -Recurse | Out-Null }
+If (-Not (Test-Path $PwshExtract)) {
+    Expand-Archive -Path $PwshZip -DestinationPath $PwshExtract
+}
+
+Join-Path $PwshExtract 'pwsh.exe'

.gitignore

@@ -0,0 +1,4 @@
+downloads/
+Output/
+TestResults.xml
+CoverageResults.xml