Adds support for creating custom Scoped Variables

[Badgerati]

Description of the Change

Adds support for creating custom Scoped Variables (like $state: and $using:), and also for converting scriptblocks in an ad-hoc manner. Adds the following functions

• Convert-PodeScopedVariables
• Convert-PodeScopedVariable
• Add-PodeScopedVariable
• Remove-PodeScopedVariable
• Test-PodeScopedVariable
• Clear-PodeScopedVariables
• Get-PodeScopedVariable
• Use-PodeScopedVariables
• Merge-PodeScriptblockArguments

Related Issue

Resolves #1207

Examples

• Using Replace syntax:

Add-PodeScopedVariable -Name 'state' `
    -SetReplace "Set-PodeState -Name '{{name}}' -Value " `
    -GetReplace "Get-PodeState -Name '{{name}}'"

• Using advanced scriptblock syntax:

Add-PodeScopedVariable -Name 'config' -ScriptBlock {
    param($ScriptBlock, $SessionState, $GetPattern, $SetPattern)
    # convert the scriptblock to a string, for searching
    $strScriptBlock = "$($ScriptBlock)"
    # the "get" template to be used, to convert "$config:Name" syntax to "(Get-PodeConfig).Name"
    $template = "(Get-PodeConfig).'{{name}}'"
    # loop through the scriptblock, replacing "$config:Name" syntax
    while ($strScriptBlock -imatch $GetPattern) {
        $getReplace = $template.Replace('{{name}}', $Matches['name'])
        $strScriptBlock = $strScriptBlock.Replace($Matches['full'], "($($getReplace))")
    }
    # convert string back to scriptblock, and return
    return [scriptblock]::Create($strScriptBlock)
}