Avoid visual glitch when terms appear for IM

This avoids a visual glitch where the Integration Manager portal would briefly
appear, but then be replaced by a smaller Terms dialog when there's something to
agree to.

To resolve this minimal code churn, this cheats a bit and customises the size of
the terms dialog to match the IM portal modal when terms are shown for IM
purposes.

Fixes https://github.com/vector-im/riot-web/issues/10386

res/css/views/dialogs/_TermsDialog.scss

@@ -14,6 +14,17 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+/*
+ * To avoid visual glitching of two modals stacking briefly, we customise the
+ * terms dialog sizing when it will appear for the integrations manager so that
+ * it gets the same basic size as the IM's own modal.
+ */
+.mx_TermsDialog_forIntegrationsManager .mx_Dialog {
+    width: 60%;
+    height: 70%;
+    box-sizing: border-box;
+}
+
 .mx_TermsDialog_termsTableHeader {
     font-weight: bold;
     text-align: left;
@@ -21,6 +32,7 @@ limitations under the License.
 
 .mx_TermsDialog_termsTable {
     font-size: 12px;
+    width: 100%;
 }
 
 .mx_TermsDialog_service, .mx_TermsDialog_summary {