Bulk convert control files. (#19986)

```
function Convert-Control {
    Param($full)
    .\vcpkg.exe format-manifest $full
    $root = $full.Substring(0, $full.Length - 7) # CONTROL
    $new = $root + 'vcpkg.json'
    $content = Get-Content -Raw $new
    $asJson = ConvertFrom-Json $content -AsHashtable -Depth 100
    $oldVersion = $asJson['port-version']
    if ($null -eq $oldVersion) {
        $oldVersionFull = $asJson['version-string']
        Write-Host "Got version $oldVersionFull"
        $match = [System.Text.RegularExpressions.Regex]::Match($oldVersionFull, '^(.+)-(\d+)$')
        if ($match.Success -and -not [System.Text.RegularExpressions.Regex]::IsMatch($oldVersionFull, '^\d\d\d\d-\d\d-\d\d$')) {
            $newFullVersion = [string]$match.Groups[1].Value
            $oldVersion = [int]$match.Groups[2].Value
            Write-Host "newFullVersion $newFullVersion oldVersion $oldVersion"
            $newVersion = $oldVersion + 1
            $asJson['version-string'] = $newFullVersion
            Write-Host "Previous version for $full extracted from version field -- setting version-string $newFullVersion and port-version $newVersion"
        } else {
            Write-Host "No previous version for $full -- setting 1"
            $newVersion = 1
        }
    } else {
        $newVersion = [int]$oldVersion + 1
        Write-Host "New version for $full : $newVersion"
    }

    $asJson['port-version'] = $newVersion

    $content = ConvertTo-Json $asJson -Depth 100
    Set-Content -Path $new -Value $content
    .\vcpkg.exe format-manifest $new
}

Get-ChildItem ports\CONTROL -Recurse | Foreach-Object {
    Convert-Control $_.FullName
}

git commit -am "this message"
.\vcpkg.exe x-add-version -all
git commit -a --amend
```

2 files changed, 15 insertions, 6 deletions

diff --git a/ports/stlab/CONTROL b/ports/stlab/CONTROL
deleted file mode 100644
index 1f6d6c858..000000000
--- a/ports/stlab/CONTROL
+++ /dev/null
@@ -1,6 +0,0 @@
-Source: stlab

-Version: 1.6.2
-Description: 

-  stlab is the ongoing work of what was Adobe Software Technology Lab.

-  The Concurrency library provides futures and channels, high level constructs for implementing algorithms that eases the use of multiple CPU cores while minimizing contention. This library solves several problems of the C++11 and C++17 TS futures.

-Build-Depends: boost-variant (osx)
\ No newline at end of file
diff --git a/ports/stlab/vcpkg.json b/ports/stlab/vcpkg.json
new file mode 100644
index 000000000..a3041dca7
--- /dev/null
+++ b/ports/stlab/vcpkg.json
@@ -0,0 +1,15 @@
+{
+  "name": "stlab",
+  "version-string": "1.6.2",
+  "port-version": 1,
+  "description": [
+    "stlab is the ongoing work of what was Adobe Software Technology Lab.",
+    "The Concurrency library provides futures and channels, high level constructs for implementing algorithms that eases the use of multiple CPU cores while minimizing contention. This library solves several problems of the C++11 and C++17 TS futures."
+  ],
+  "dependencies": [
+    {
+      "name": "boost-variant",
+      "platform": "osx"
+    }
+  ]
+}