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/css/views/dialogs/_JoinRuleDropdown.pcss

@@ -0,0 +1,66 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_JoinRuleDropdown {
+    margin-bottom: 8px;
+    font-weight: normal;
+    font-family: $font-family;
+    font-size: $font-14px;
+    color: $primary-content;
+
+    .mx_Dropdown_input {
+        border: 1px solid $input-border-color;
+    }
+
+    .mx_Dropdown_option {
+        font-size: $font-14px;
+        line-height: $font-32px;
+        height: 32px;
+        min-height: 32px;
+
+        > div {
+            padding-left: 30px;
+            position: relative;
+
+            &::before {
+                content: "";
+                position: absolute;
+                height: 16px;
+                width: 16px;
+                left: 6px;
+                top: 8px;
+                mask-repeat: no-repeat;
+                mask-position: center;
+                background-color: $secondary-content;
+            }
+        }
+    }
+
+    .mx_JoinRuleDropdown_invite::before {
+        mask-image: url('$(res)/img/element-icons/lock.svg');
+        mask-size: contain;
+    }
+
+    .mx_JoinRuleDropdown_public::before {
+        mask-image: url('$(res)/img/globe.svg');
+        mask-size: 12px;
+    }
+
+    .mx_JoinRuleDropdown_restricted::before {
+        mask-image: url('$(res)/img/element-icons/group-members.svg');
+        mask-size: contain;
+    }
+}