Use `chdir = TRUE` when sourcing R scripts

System details:

Positron and OS details:

Positron Version: 2025.03.0 build 46
Code - OSS Version: 1.96.0
Commit: 99f36c653f7570b325f6f9f8712052405a05426f
Date: 2025-02-18T23:38:56.252Z
Electron: 32.2.6
Chromium: 128.0.6613.186
Node.js: 20.18.1
V8: 12.8.374.38-electron.0
OS: Darwin arm64 24.3.0

Interpreter details:

any

Describe the issue:

R scripts are sourced in the current working directory.

Steps to reproduce the issue:

1. Open an .R file in Positron
2. Change to a directory other than the one in which the .R file resides, e.g. setwd("~")
3. Add the following to the file: print(getwd())
4. From the Command Palette, run the R: Source R File command (Cmd + Shift + S)

The script prints the current directory, not the directory of the script.

Expected or desired behavior:

The script should be run in the context of its own directory -- like notebooks, scripts are easier to write when they're run in a predictable working directory. We could use the chdir = TRUE argument to R's source() command to accomplish this.

This behavior should probably be optional since there are likely cases where you want a script to run against your current directory.

Start at the implementation of the Command Palette's “R: Source R File” command and trace how it invokes R's source() function. Check for existing tests around sourcing scripts; done means sourcing an .R file uses its own directory by default while preserving a clearly defined way to use the current working directory.