[Lens] [Dashboard] Remove metric chart progress bar rounded border (#211189)

## Summary

Closes https://github.com/elastic/kibana/issues/174889

1. Removes rounded border shown in metric chart progress bar border
2. Makes the panel heading highlight fit the container
3. Removes rounded border from loader horizontal bar

## Screenshots and screen recordings

1. Removes rounded border shown in metric chart progress bar border

#### Before
<img width="874" alt="Screenshot 2025-02-14 at 21 05 29"
src="https://github.com/user-attachments/assets/ada89180-0cb1-4385-b58d-a6ca068376b7"
/>

#### After

<img width="647" alt="Screenshot 2025-02-14 at 20 30 58"
src="https://github.com/user-attachments/assets/9048a1a5-6afd-418f-994c-69fd68b969b1"
/>/

2. Makes the panel heading highlight fit the container

#### Before

<img width="950" alt="Screenshot 2025-02-14 at 20 34 31"
src="https://github.com/user-attachments/assets/eb4df553-bace-4ce2-b2c0-93829235c5ce"
/>

#### After

<img width="154" alt="Screenshot 2025-02-14 at 20 36 53"
src="https://github.com/user-attachments/assets/2887de13-198d-4ea4-a7a9-57bfd657746f"
/>/

3. Removes rounded border from loader horizontal bar

#### Before


https://github.com/user-attachments/assets/a091f3a1-9d0e-4a55-a45e-9930e6d54983


#### After


https://github.com/user-attachments/assets/5e6fd8d4-407e-45c0-b3ff-ba1884c413c1

### Considerations

We need to make sure that these styles changes do not affect the rest of
the visualizations. I checked different visualizations and it looks like
there are no side effects, e.g metric chart - break down by

<img width="653" alt="Screenshot 2025-02-14 at 20 48 15"
src="https://github.com/user-attachments/assets/d21b6e5d-af53-48be-ac20-646468949fea"
/>
<img width="650" alt="Screenshot 2025-02-14 at 21 03 29"
src="https://github.com/user-attachments/assets/c60d1ca4-671b-492d-8629-5a69e273dc89"
/>

### Checklist

- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

src/platform/plugins/private/presentation_panel/public/panel_component/presentation_panel_internal.tsx

@@ -186,6 +186,7 @@ const styles = {
     flexDirection: 'column',
     height: '100%',
     position: 'relative',
+    overflow: 'hidden',
   }),
   embPanelContent: css({
     '&.embPanel__content': {
@@ -193,7 +194,6 @@ const styles = {
       flex: '1 1 100%',
       zIndex: 1,
       minHeight: 0, // Absolute must for Firefox to scroll contents
-      borderRadius: '4px',
       overflow: 'hidden',
     },
     '&.embPanel__content--hidden, &[data-error]': {

x-pack/platform/plugins/shared/lens/public/editor_frame_service/editor_frame/workspace_panel/workspace_panel_wrapper.scss

@@ -24,6 +24,7 @@
     border-radius: $euiBorderRadius;
     background: $euiColorEmptyShade;
     height: 100%;
+    overflow: hidden;
     @include euiScrollBar;
     &>* {
       flex: 1 1 100%;

x-pack/platform/plugins/shared/lens/public/visualization_container.scss

@@ -10,8 +10,6 @@
   height: 100%;
   display: flex;
   overflow: auto;
-  // important for visualizations with no padding
-  border-radius: $euiBorderRadius;
   @include euiScrollBar;
   .lnsExpressionRenderer__component {
     position: static; // Let the progress indicator position itself against the outer parent