Issue: Smart Variable Rename

PR Summary

This pull request implements the LSP textDocument/rename and textDocument/prepareRename handlers for PowerShell.

#2152 exposes the related service settings in vscode-powershell.

Reviewer's Guide

PowerShell is not a statically typed language and as such, some variable definitions and relations are determined at runtime, therefore true static analysis of a full PowerShell project is not possible. However, by presenting a disclaimer of the limitations, we feel we can provide fairly stable rename support within a single document for several scenarios without turning this into a bug/issue farm.

All work is driven through a RenameService which controls the messaging and registers the handlers. The general flow is to:

1. Identify if a symbol at least meets the basic criteria for a rename, as a performance optimization
2. Find the original definition/assignment where the target symbol is referenced
3. Use that as an anchor for all renames in the document.

The RenameHandlerTests and PrepareRenameHandlerTests follow the rename behavior, and the Handler is considered our public API for these purposes and what we test against, even though there is a lot of implementation detail inside.

Taking this approach minimizes state maintenance in the Service at the expense of probably more-than-necessary AST walks, but current testing performance finds this to be sufficient even for large documents. There are several places caching of some AST walks could be performed to optimize performance but they are out of scope for this initial PR.

Reviewer Asks

• Identify areas where there is a public PowerShell API where logic is being duplicated that could be replaced with the API instead
• Find edge cases/scenarios that we should be able to reasonably cover, if not, we will add them to the exclusions.

TODO List

• Replaced Custom LSP calls with OmniSharp IPrepareRenameHandler and IRenameHandler
• Use custom ScriptExtentAdapter and ScriptPositionAdapter types to translate between script and lsp positions to avoid "off-by-one" errors since lsp is zero-based and script is one-based
• Tests for PrepareRenameProvider and RenameProvider
• Deduplicate PrepareRenameProvider and RenameProvider logic
• Add Configuration Support via Omnisharp ILanguageServerConfiguration
• Create Settings for Function and Variable Aliases and pass thru the info to LSP
• Wire up Settings to actually work
• Add Message Support via ILanguageServerFacade
• Present Risk Warning and acceptance via LSP ShowMessageRequest (cannot set the setting directly ATM as it's not an LSP standard scenario)
• Rewrite IterativeFunctionVisitor to an AstVisitor
• Rewrite IterativeVariableVisitor to an AstVisitor
• Finish fixing tests
• Add more "sad path" tests for things that should not get triggered for rename
• Add E2E tests for testing the actual rename process
• Validate FunctionName and VariableName to be valid before passing through
• Support scope modifiers (e.g. $GLOBAL, $SCRIPT, etc.)
• Evaluate against PSScriptAnalyzer rules to use consistent discovery methods if reasonable

Potential Additional Features

• Simple conditional splat parameter rename.

function Do-Thing($test) {} #test should rename
$x = @{test = 2} #test here should rename
$x.test = 5 #Test here should rename
Do-Thing @x

• Renaming $_ or $PSItem can place a $_ = or $PSItem = at the top of the scope. (I would use this a lot and seems pretty reasonable to do, but we would need an implicit definition of $PSItem in the current structure since we require a definition)

More Tests

• Space in variable or function rename request should fail "$va riable" along with any other invalid characters for a rename
• Parameter, Function, and Variable renames where they are not defined in scope should fail
• Renaming a parameter and removing the '-' should still work