Move Flex & Box component into shared component folder (#30357)

* refactor: move Flex component in shared components

* refactor: update imports

* refactor: remove Flex pcss file

* fix: Flex component css override

* test: update snapshots

* fix: html export

* chore: add css module support to jest

* chore: keep old copyright

* refactor: change `mx_Flex` in `ErrorView` to `mx_ErrorView_flexContainer`

* test: update snapshots

* refactor: move Box component in shared components

* refactor: update import and css override

* test: update snapshots

src/utils/exportUtils/HtmlExport.tsx

@@ -161,7 +161,7 @@ export default class HTMLExporter extends Exporter {
                     <div class="mx_MatrixChat_wrapper" aria-hidden="false">
                         <div class="mx_MatrixChat">
                         <main class="mx_RoomView">
-                            <div class="mx_Flex mx_RoomHeader light-panel">
+                            <div class="mx_RoomHeader light-panel">
                                 ${roomAvatar}
                                 <div class="mx_RoomHeader_infoWrapper">
                                     <div

src/utils/exportUtils/exportCustomCSS.css

@@ -131,11 +131,11 @@ a.mx_reply_anchor:hover {
 }
 
 .mx_RoomHeader {
-    --mx-flex-display: flex;
-    --mx-flex-direction: row;
-    --mx-flex-align: center;
-    --mx-flex-justify: start;
-    --mx-flex-gap: var(--cpd-space-3x);
+    display: flex;
+    flex-direction: row;
+    align-items: center;
+    justify-content: start;
+    gap: var(--cpd-space-3x);
 }
 
 .mx_ReplyChain_Export {