Remove gulp-sass; bump gulp and tether deps

[ericyd]

Draft

Leaving this as a draft until I can test it properly

Motivation

Allow leadconduit-client to use npm 9.

gulp-sass v2 is just not a feasible option with our modern hardware and runtimes. Installing it is impossible.

In addition: we have barely ever touched the CSS in this repo; we can just use the compiled CSS as a starting point, and modify as needed over time.

Description of the change

1. Remove gulp-sass.
   • Why?: gulp-sass is incredibly difficult to install with npm 9 and modern hardware.
2. Replace .sass files with their compiled .css equivalents from dist
   • Why?: We rarely (never?) need to update the CSS in this lib, and we don't really need the SASS functionality that the library depended on. If we need specific fixes, we can just do it in the plain CSS.
3. Bump gulp to v4, and update Gulpfile to reflect new syntax
   • Why?: gulp 3 was throwing a bizarre error, it probably isn't compatible with node 18
4. Bump tether to 2.0.0
   • Why?: we were pinned to a forked version of tether and I'm not sure why, the changes introduced on the fork were extremely minimal. In addition, that version of tether was also pinned to gulp-sass and other deprecated dependencies. Installing these were going to be a pain. [email protected] removed gulp and other difficult dependencies, and according to the release notes does not introduce any breaking changes. Testing shall prove if this is correct or not!!!

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Configuration change
• Technical Debt
• Documentation

Related tickets

https://app.shortcut.com/active-prospect/story/62992/update-client-to-node-18-npm-9

Checklists

Development and Testing

• [N/A] Lint rules pass locally.
• [N/A] The code changed/added as part of this pull request has been covered with tests, or this PR does not alter production code.
• [N/A] All tests related to the changed code pass in development, or tests are not applicable.

Code Review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached.
• At least two engineers have been added as "Reviewers" on the pull request.
• Changes have been reviewed by at least two other engineers who did not write the code.
• This branch has been rebased off master to be current.

Tracking

• Issue from Shortcut/Jira has a link to this pull request.
• This PR has a link to the issue in Shortcut.

QA

• This branch has been deployed to staging and tested.

[shortcut-integration]

This pull request has been linked to Shortcut Story #62992: update client to Node 18/npm 9.

[ericyd]

this won't work. Either

1. we stick with tether v1.4.x which uses gulp-sass v2, or
2. we update to tether v2, which breaks this lib.

Without substantially re-writing this lib ourselves, there will be no way to make tether-drop work without a gulp-sass dependency