PS: Extract source files found via PSModulePath

[MathiasVP]

PowerShell has a peculiar feature of "implicit module imports".

From https://learn.microsoft.com/en-us/powershell/scripting/developer/module/importing-a-powershell-module?view=powershell-7.4#implicitly-importing-a-module-powershell-30:

[...] modules are imported automatically when any cmdlet or function in the module is used in a command. This feature works on any module in a directory that is included in the value of the PSModulePath environment variable.

So when we see an invocation such as:

Foo 42

this may refer to a command defined in a file totally outside the source directory, and will be implicitly loaded into the current Powershell session.

To handle such scenarios this PR does several things:

• It adds extraction of the files inside the directories pointed to by the PSModulePath environment variable. This can be disabled via a command-line argument to the extractor, but is enabled by default.
• It adds .psd1 to the list of file extensions to extract, which are module manifest files. These module manifest files contain the information necessary to detect this "implicit loading"
• Finally, we add a new extensional to check whether a source file was found via the PSModulePath environment variable.