versioning: transition from nerdbank to version file (#1231)

With the [plan to migrate GCM to a formula for release via
`Homebrew/homebrew-core`](#1102),
it became clear that
[Nerdbank.GitVersioning](https://github.com/dotnet/Nerdbank.GitVersioning)
was no longer an option for versioning the project. This is because
`Nerdbank.GitVersioning` requires history to calculate things like ['Git
height'](https://github.com/dotnet/Nerdbank.GitVersioning#what-is-git-height),
and the formula requires a tarball to build, which, of course, has no
history.

This change pivots GCM to the simpler strategy of using a version
specified in a `VERSION` file at root. This version will be updated by
maintainers prior to release - giving them more granular control of
versioning, which in turn allows for versioning to be more predictable
(i.e. maintainers will know what the version will be before publication
of the release).

The version specified in the file is the one slated for the next
release: `2.1.0.0`.

**Note:** This change [fails on
Windows](https://github.com/ldennington/git-credential-manager/actions/runs/4824686907)
due to a [bug in
MSAL](AzureAD/microsoft-authentication-library-for-dotnet#4108)
unless we ensure all projects have at least 1 dependency. We are working
around this issue by adding Newtonsoft.Json as this dependency (since we
were already shipping it anyway).

.github/workflows/codeql-analysis.yml

@@ -22,10 +22,7 @@ jobs:
         language: [ 'csharp' ]
 
     steps:
-    - name: Checkout repository
-      uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
-      with:
-        fetch-depth: 0 # patch around Nerdbank.GitVersioning failure
+    - uses: actions/checkout@v3
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL

.github/workflows/continuous-integration.yml

@@ -17,9 +17,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
 
     steps:
-    - uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
-      with:
-        fetch-depth: 0 # Indicate full history so Nerdbank.GitVersioning works.
+    - uses: actions/checkout@v3
 
     - name: Setup .NET
       uses: actions/[email protected]

.github/workflows/lint-docs.yml

@@ -18,7 +18,7 @@ jobs:
     name: Lint markdown files
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
+      - uses: actions/checkout@v3
 
       - uses: DavidAnson/markdownlint-cli2-action@cdfad95cc96588c74b62ad2d3f2e1772090099ac
         with:
@@ -30,7 +30,7 @@ jobs:
     name: Check for broken links
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
+      - uses: actions/checkout@v3
 
       - name: Run link checker
         # For any troubleshooting, see: