feat: add variable substitution support for vscode's ${workspaceFolder:x}

[tomlau10]

resolves #2987

---

implementation details: #2987 (comment)

• workspace folder names are captured from client's initialization request param workspaceFolders[].name
• if provided, it is then stored into the created workspace.scope object
• finally when resolving a ${workspaceFolder:x} path placeholder
  use the decoded uri of the workspace.scope object that having x as the folder name
  (which becomes absolute path of that folder)

Example

• a dummy _.code-workspace

{
	"folders": [
		{
			"name": "root",
			"path": "."
		},
		{
			"name": "client",
			"path": "client"
		},
		{
			"name": "server",
			"path": "server"
		}
	],
	"settings": {
		"Lua.workspace.library": [
			"${workspaceFolder:client}",
		]
	}
}

• upon inspecting log file, the client is sending the following to server during init

  workspaceFolders = { {
      name = "root",
      uri = "file:///c%3A/Users/TomLau/test"
    }, {
      name = "client",
      uri = "file:///c%3A/Users/TomLau/test/client"
    }, {
      name = "server",
      uri = "file:///c%3A/Users/TomLau/test/server"
    } }

• therefore ${workspaceFolder:client} will be resolved as furi.decode('file:///c%3A/Users/TomLau/test/client')
  which becomes C:\Users\TomLau\test\client