MDC Migration: remove padding to individual dialogs in favor of global padding setting (#6690)

## Motivation for features / changes
For consistency it would be better to have a global padding setting. The
old mat-dialog had a default padding. During migration we added padding
to a few components but we missed one. Internally we also have many more
dialogs which look broken after migration. The global setting is less
code to maintain and gives our dialogs consistency.

I added the global setting in #6689 but realized the stacking of the
previously added padding during migration made some of the dialogs look
bad.

## Screenshots of UI changes (or N/A)
![Screenshot 2023-12-01 at 3 38
31 PM](https://github.com/tensorflow/tensorboard/assets/8672809/bc288a0d-e495-4a0d-bad7-e7600ddbc916)

<img width="427" alt="Screenshot 2023-12-04 at 3 00 08 PM"
src="https://github.com/tensorflow/tensorboard/assets/8672809/524ec2c4-3d66-49ef-a681-4cb26c5cab56">


![Screenshot 2023-12-01 at 3 40
41 PM](https://github.com/tensorflow/tensorboard/assets/8672809/9d417abb-4103-4d82-bec8-38dc475f7f34)

Author: JamesHollyer

tensorboard/webapp/runs/views/runs_table/regex_edit_dialog_component.scss

@@ -28,11 +28,11 @@ $padding-size: 16px;
       @include tb-theme-foreground-prop(color, link-visited);
     }
   }
-  padding: $padding-size;
+  padding-bottom: $padding-size;
 }
 
 .group-container {
-  margin: $padding-size;
+  margin: $padding-size 0;
 
   h4 {
     margin-bottom: $padding-size;

tensorboard/webapp/settings/_views/settings_dialog_component.css

@@ -17,12 +17,11 @@ limitations under the License.
 }
 
 :host > div {
-  margin: 16px;
+  margin: 16px 0;
 }
 
 h3 {
   font-size: 20px;
-  margin: 16px;
 }
 
 .reload-toggle {

tensorboard/webapp/theme/_tb_theme.template.scss

@@ -287,7 +287,7 @@ $tb-dark-theme: map_merge(
     // new dialog this padding was added to avoid adding it to them all
     // individually.
     .mat-mdc-dialog-surface {
-      padding: 24px;
+      padding: 16px;
     }
   }