Issue #3278415 by nod_, lauriii, catch, Wim Leers, longwave, xjm, claudiu.cristea: Remove usages of the JavaScript ES6 build step, the build step itself, and associated dev dependencies

Issue #3263823 by Spokje, nod_, kostyashupenko, murilohp, adityasingh, pooja saraah, ravi.shankar, catch: Empty out and deprecate drupal libraries which are related to Internet Explorer 11 polyfills in 10.0.x for removal in 11.0.0

Revert "Issue #3263823 by Spokje, nod_, kostyashupenko, murilohp, adityasingh, pooja saraah, ravi.shankar: Empty out and deprecate drupal libraries which are related to Internet Explorer 11 polyfills in 10.0.x for removal in 11.0.0"

This reverts commit 99059eda.

Issue #3263823 by Spokje, nod_, kostyashupenko, murilohp, adityasingh, pooja saraah, ravi.shankar: Empty out and deprecate drupal libraries which are related to Internet Explorer 11 polyfills in 10.0.x for removal in 11.0.0

Revert "Issue #3238501 by kostyashupenko, Spokje, mherchel, nod_, longwave, lauriii, bnjmnm: Remove Internet Explorer 11 polyfills"

This reverts commit 145d7286.

Issue #3238501 by kostyashupenko, Spokje, mherchel, nod_, longwave, lauriii, bnjmnm: Remove Internet Explorer 11 polyfills

Issue #3117698 by mherchel, anmolgoyal74, lauriii, kapilkumar0324, andrewmacpherson: Allow PostCSS Plugin “Px to Rem” in core for Olivero theme

Issue #3085245 by bnjmnm, narendra.rajwar27, lauriii, olli: Un-inline SVGs in pcss.css files, add build tool to inline them when compiled

Issue #3155159 by laura.gates, jhodgdon, Kristen Pol: Fix notice at top of generated CSS files from PCSS

Issue #3101543 by lauriii, bnjmnm, ravi.shankar, alexpott: Update core JavaScript dependencies listed in package.json

Issue #3060153 by lauriii, alexpott, finnsky, Wim Leers, xjm, catch: Use PostCSS in core, initially only for Claro