Rename PostCSS files to .pcss (#9013)

* Rename PostCSS files to `.pcss`

* Make Stylelint happy

* Delint

* Rename new files too

* delint

* Fix bad comment placement

res/themes/legacy-light/css/_fonts.pcss

@@ -14,7 +14,7 @@
 
 // Grab the other fonts from the current theme, so we can override to Inter
 // in custom fonts if needed.
-@import "../../light/css/_fonts.scss";
+@import "../../light/css/_fonts.pcss";
 
 // Nunito as the default, for old time's sake on legacy themes.
 /* the 'src' links are relative to the bundle.css, which is in a subdirectory.

res/themes/legacy-light/css/_paths.pcss

@@ -1,3 +1,3 @@
-// Path from root SCSS file (such as `light.scss`) to `res` dir in the source tree
+// Path from root SCSS file (such as `light.pcss`) to `res` dir in the source tree
 // This value is overridden by external themes in `element-web`.
 $res: ../../..;

res/themes/legacy-light/css/legacy-light.pcss

@@ -0,0 +1,6 @@
+@import "../../../../res/css/_font-sizes.pcss";
+@import "_paths.pcss";
+@import "_fonts.pcss";
+@import "_legacy-light.pcss";
+@import "../../../../res/css/_components.pcss";
+@import url("highlight.js/styles/atom-one-light.css");

res/themes/legacy-light/css/legacy-light.scss

@@ -1,6 +0,0 @@
-@import "../../../../res/css/_font-sizes.scss";
-@import "_paths.scss";
-@import "_fonts.scss";
-@import "_legacy-light.scss";
-@import "../../../../res/css/_components.scss";
-@import url("highlight.js/styles/atom-one-light.css");