Normalize Rojo sourcemap paths relative to its location

[jeparlefrancais]

Closes #116

This makes the sourcemap paths relative to the sourcemap location itself.

• [x] add entry to the changelog

[github-actions[bot]]

Coverage after merging rojo-sourcemap-relative into main will be

89.36%

Coverage Report for Changed Files

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src/rules/convert_require
mod.rs	84.86%	100%	72.73%	87.50%	104–106, 129, 139–140, 150, 40, 51, 61–62, 87
roblox_require_mode.rs	57.71%	100%	57.89%	57.69%	102–105, 107, 110–112, 114, 120–121, 154–161, 164–172, 176, 181–185, 188, 192–197, 200–207, 220–223, 42, 57–64, 74–76, 90–92
rojo_sourcemap.rs	95.77%	100%	83.33%	97.44%	93, 98