Miscellaneous fixes.

[mjr4077au]

Variety of fixes that were hard to include unti the release occurred so I could rebase and diff my side compared to yours.

The supply of these fixes, the other two PRs, and the outstanding PowerShell 7 PR effectively eliminate any need I've had for maintaining my own fork.

• Fix some more variables under strict mode.
  • The variable $installPhase is used by Write-Log before it's defined.
  • The variable $logName is accessed by `Write-Log before it's defined.
  • The variable $defaultMsiExecutablesList is accessed irrespective of whether an MSI operation is underway, so it needs to be available globally, albeit null.
  • The variable $oldPSWindowTitle is accessed in Exit-Script, potentially before its defined.
• Fix bad variable scoping for $runningProcessDescriptions.
  • The previous setup was breaking strict mode.
• Ensure $deploymentType is always title-cased for aesthetics.
• Ensure $deployModeNonInteractive is defined, even for silent mode.
  • It can be accessed in silent modes, but if it doesn't exist this will throw strict mode.
• Rename Zerotouch to Zero-Config to be consistent with the rest of the log messages.
• Fix bad call to a Dispose() method, which accepts no parameters.
• Ensure $installTitle is appropriately trimmed.
  • Variables like $appVendor and $appVersion aren't mandatory, so if they're empty they can leave spaces in $installTitle.
• Remove dead block of code.
  • Because $configDeferPromptNoDeadline is not defined, this was causing a throw in strict mode. If the block ever triggered, it was also adding a new line for no reason.
• Fix bad try/catch setup in Get-ServiceStartMode.
  • There was no need for the try/catch setup at all, can simply use a better -ErrorAction value here. This was also causing noise in the $Error global array.
• Import assemblies earlier in case they're needed within Extensions.
• Only set $DefaultMstFile and $DefaultMspFiles if they're not already defined.
  • If someone's doing something specific in the Extensions file (i.e. me), they might already be defined ahead of time.

Before submitting this Pull Request, I made sure:

• [X] I tested the toolkit with my changes and made sure it doesn't break other code.
• [X] I updated the documentation with the changes I made.
• [X] The code I changed has comments with explanation.
• [X] The encoding of the file wasn't changed. It is still UTF8 with BOM.