Add sourceMapRelativePaths option for portable sourcemaps

[bartvandenende-wm]

Summary

Adds a new sourceMapRelativePaths bsconfig option that emits relative file paths in sourcemap sources instead of absolute paths. This makes sourcemaps portable across different machines and CI environments.

Resolves #1156

Problem

Sourcemaps currently embed absolute paths (e.g. /home/runner/work/project/src/main.bs). When build output is moved to another machine -- for example when libraries are published to npm and consumed elsewhere -- these paths no longer resolve and debugging tools cannot locate the original source files.

Solution

A new boolean config option sourceMapRelativePaths (default: false) post-processes the generated sourcemap at serialization time, converting absolute sources entries to paths relative to the .map file location. For example:

// Before (absolute)
{ "sources": ["/Users/dev/project/src/source/main.bs"] }

// After (relative, with sourceMapRelativePaths: true)
{ "sources": ["../../src/source/main.bs"] }

VSCode extension compatibility

In the issue, @TwitchBronBron noted:

I think we needed absolute paths because of the way the vscode extension moves files around.

After inspecting the roku-debug source, this concern does not apply. The SourceMapManager.set() method already resolves source paths using path.resolve():

parsedSourceMap.sources = parsedSourceMap.sources.map(source => fileUtils.standardizePath(
    path.resolve(
        //use the map's sourceRoot, or the map's folder path (to support relative paths)
        parsedSourceMap.sourceRoot || path.dirname(sourceMapPath),
        source
    )
));