Update project to gulp-sass@5

[Splaktar]

Discuss the use-case or motivation for changing the existing behavior

This is blocked by #12113 as gulp-sass@5 requires gulp@4.

One of the reasons we need to support the new sass package is mentioned in PR #12112:

DEPRECATION WARNING: Using / for division is deprecated and will be removed in Dart Sass 2.0.0.

Recommendation: math.div($button-fab-height - $button-fab-padding, 2)

More info and automated migrator: https://sass-lang.com/d/slash-div

    ╷
345 │   @include fab-position(bottom-right, auto, ($button-fab-width - $button-fab-padding)/2, ($button-fab-height - $button-fab-padding)/2, auto);
    │                                                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    node_modules\angular-material\angular-material.scss 345:90  fab-all-positions()
    node_modules\angular-material\angular-material.scss 2000:5  @import

List the affected versions of AngularJS, Material, OS, and browsers

• AngularJS: 1.8.2
• AngularJS Material: 1.2.3
• OS: all
• Browsers: all
• Screen Readers: all

Add anything else we should know

Here's the migration guide: https://github.com/dlmanning/gulp-sass#migrating-to-version-5

[Splaktar]

Based on PR #12131, this doesn't seem to be blocked by gulp@4 afterall.