Revert "Merge branch 'switch-to-sassc' into 'master'"

Closes #26762

See merge request !8642

# Conflicts:
#	app/assets/javascripts/vue_pipelines_index/stage.js.es6

Speed up dashboard milestone index by scoping IssuesFinder to user authorized projects

See merge request !8524

Add Slack slash commands to project services list index

See merge request !8636

Shows current user on top of filtered dropdown list

Closes #26765

See merge request !8612

Fix search bar filter dropdown scrollbars

Closes #26777

See merge request !8615

Fixes big pipeline and small pipeline width problems

Closes #26667

See merge request !8593

better UI fix - simple solution - pipelines#index mini_graph in Vue

See merge request !8614

correct User-agent placement in robots.txt

Closes #26807

See merge request !8623

Refactor cycle analytics stages (1st iteration)

See merge request !7647

Time tracking API

Closes #25861

See merge request !8483

Add a `:repository` trait to the `:empty_project` factory

See merge request !8605

Resolve "Wrong file size on repository page"

Closes #26773

See merge request !8616

Correctly keeps merge request tabs in place when editting value in

See merge request !8595

Correct documentation for `data_attribute` method

See merge request !8603

Backport timetracking to CE

See merge request !8195

Fixing typo

See merge request !8621

Fix Compare page throws 500 error when any branch/reference is not selected

Closes #25814

See merge request !8523

Remove some useless require_relative statements

Closes #26756

See merge request !8609

Disable all cops in .rubocop_todo.yml

See merge request !8610

Support `/merge` slash command for MRs

Closes #24915

See merge request !7746

Use cached values to compute total issues count in milestone index pages

See merge request !8518

Do not show artifacts keep button if not allowed

Closes #26357

See merge request !8501

Show 'too many changes' message for merge request

Closes #25017

See merge request !8444

Remove rerun since it's not used anymore

Closes #19633

See merge request !8598

Synchronize all project authorization refreshing work using a lease

Closes #25987

See merge request !8599

Fixed random issue boards sidebar failure

Closes #26751

See merge request !8602

Update ffaker to ~>2.4 to avoid generating names with suffixes

Closes #26492

See merge request !8596

Fix search group/project filtering to show results

Closes #26616

See merge request !8565

Pipeline Index Mini Graph Fix

See merge request !8542

Ensure updating project settings shows a flash message on success

See merge request !8579

Resolve "Add Hover animations"

Closes #26207

See merge request !8415

Retain original casing for  build name in manual pipeline dropdown

Closes #25946

See merge request !8387

Switch to sassc-rails

Closes #18432

See merge request !8556

Closes #18432

This uses sassc to compile the application's SASS so it compiles faster.

Without attempting to be very scientific here are some numbers I got:

Using sassc-rails:

```
[1] pry(main)> Benchmark.bm { |bm| bm.report { Rails.application.assets["application.css"] } }
       user     system      total        real
   1.430000   0.380000   1.810000 (  1.830753)
```

Using sass-rails:
```
[1] pry(main)> Benchmark.bm { |bm| bm.report { Rails.application.assets["application.css"] } }
       user     system      total        real
  12.320000   0.530000  12.850000 ( 12.909684)
```

The result is faster page loads when changing CSS in development and
faster precompilation.

Remove rerun since it's not used anymore

Closes #19633

See merge request !8598

Synchronize all project authorization refreshing work using a lease

Closes #25987

See merge request !8599

Fixed random issue boards sidebar failure

Closes #26751

See merge request !8602