[heft-sass-plugin] Add doNotTrimOriginalFileExtension option

[iclanton]

Summary

Adds a doNotTrimOriginalFileExtension option to heft-sass-plugin. When enabled, the original source file extension is preserved in the CSS output filename. For example, styles.scss emits styles.scss.css instead of styles.css.

Details

Previously, the plugin always stripped the original extension before appending .css, so styles.module.scss would produce styles.module.css. Some consumers need the original extension retained in the output path (e.g. to avoid filename collisions when multiple input extensions map to the same base name, or to match an expected import path convention).

The option is wired through ISassConfigurationJson in SassPlugin.ts → ISassProcessorOptions in SassProcessor.ts, where the branching logic in CSS output path generation was already added.

A new build-test project (heft-sass-doNotTrimOriginalFileExtension-test) exercises the option end-to-end: it configures doNotTrimOriginalFileExtension: true and uses Jest snapshot tests to assert that the CSS output files carry the original extension (e.g. styles.module.scss.css, stylesGlobal.global.scss.css).

How it was tested

The new heft-sass-doNotTrimOriginalFileExtension-test build-test project will be built as part of CI. Snapshots will be committed after the initial build to lock in the expected output filenames.