fix: projectRoot passed to vecLib was malformed (#1250)

## Problem
workspace folder was not being correctly parsed, which caused incorrect projectRoot to be sent to vector index

This caused the relativePaths in relevantTextDocuments to be incorrect

## Solution
Parse workspaceFolder URI

Tested on Mac and Windows

Author: avi-alpert

server/aws-lsp-codewhisperer/src/shared/localProjectContextController.ts

@@ -218,7 +218,7 @@ export class LocalProjectContextController {
                     this.maxIndexSizeMB
                 )
 
-                const projectRoot = this.workspaceFolders.sort()[0].uri
+                const projectRoot = URI.parse(this.workspaceFolders.sort()[0].uri).fsPath
                 await this._vecLib?.buildIndex(sourceFiles, projectRoot, 'all')
                 this.log.info('Context index built successfully')
             }