Add report room dialog button/dialog. (#29513)

* Add report room dialog button/dialog.

* Update copy

* fixup tests / lint

* Fix title in test.

* update snapshot

* Add unit tests for dialog

* lint

test/unit-tests/components/views/dialogs/__snapshots__/ReportRoomDialog-test.tsx.snap

@@ -0,0 +1,100 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ReportRoomDialog displays admin message 1`] = `
+<div>
+  <div
+    data-focus-guard="true"
+    style="width: 1px; height: 0px; padding: 0px; overflow: hidden; position: fixed; top: 1px; left: 1px;"
+    tabindex="0"
+  />
+  <div
+    aria-describedby="mx_ReportEventDialog"
+    aria-labelledby="mx_BaseDialog_title"
+    class="mx_ReportRoomDialog mx_Dialog_fixedWidth"
+    data-focus-lock-disabled="false"
+    role="dialog"
+  >
+    <div
+      class="mx_Dialog_header"
+    >
+      <h1
+        class="mx_Heading_h3 mx_Dialog_title"
+        id="mx_BaseDialog_title"
+      >
+        Report Room
+      </h1>
+    </div>
+    <form
+      class="_root_19upo_16"
+      id="mx_ReportEventDialog"
+    >
+      <p>
+        Report this room to your homeserver admin. This will send the room's unique ID, but if messages are encrypted, the administrator won't be able to read them or view shared files.
+      </p>
+      <p>
+        <h1>
+          You should know
+        </h1>
+        
+
+        <p>
+          This doesn't actually go 
+          <strong>
+            anywhere
+          </strong>
+          .
+        </p>
+        
+
+      </p>
+      <div
+        class="_field_19upo_26"
+      >
+        <label
+          class="_label_19upo_59"
+          for="mx_ReportRoomDialog_reason"
+        >
+          Reason
+        </label>
+        <textarea
+          id="mx_ReportRoomDialog_reason"
+          placeholder=" Reason for reporting..."
+          rows="5"
+        />
+      </div>
+      <div
+        class="mx_Dialog_buttons"
+      >
+        <span
+          class="mx_Dialog_buttons_row"
+        >
+          <button
+            data-testid="dialog-cancel-button"
+            type="button"
+          >
+            Cancel
+          </button>
+          <button
+            class="mx_Dialog_primary"
+            data-testid="dialog-primary-button"
+            type="button"
+          >
+            Send report
+          </button>
+        </span>
+      </div>
+    </form>
+    <div
+      aria-label="Close dialog"
+      class="mx_AccessibleButton mx_Dialog_cancelButton"
+      role="button"
+      tabindex="0"
+    />
+  </div>
+  <div
+    data-focus-guard="true"
+    style="width: 1px; height: 0px; padding: 0px; overflow: hidden; position: fixed; top: 1px; left: 1px;"
+    tabindex="0"
+  />
+</div>
+`;