[9.1] [Discover] Fix font size in a single document/flyover popover (#226259) (#226348)

# Backport

This will backport the following commits from `main` to `9.1`:
- [[Discover] Fix font size in a single document/flyover popover
(#226259)](#226259)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

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Fix font size in a single document/flyover popover (#226259)\n\n##
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Fix font size in a single document/flyover
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Fix font size in a single document/flyover popover (#226259)\n\n##
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Fix font size in a single document/flyover popover (#226259)\n\n##
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BACKPORT-->

Co-authored-by: Ania Kowalska <[email protected]>

Author: kibanamachine

src/platform/plugins/shared/unified_doc_viewer/public/components/doc_viewer_table/table_cell_value.tsx

@@ -16,6 +16,7 @@ import {
   EuiTextColor,
   EuiToolTip,
   useResizeObserver,
+  euiFontSize,
   type UseEuiTheme,
 } from '@elastic/eui';
 import React, { Fragment, useCallback, useState } from 'react';
@@ -200,18 +201,22 @@ export const TableFieldValue = ({
 };
 
 const componentStyles = {
-  docViewerValue: ({ euiTheme }: UseEuiTheme) =>
-    css({
+  docViewerValue: (themeContext: UseEuiTheme) => {
+    const { euiTheme } = themeContext;
+    const { fontSize } = euiFontSize(themeContext, 's');
+
+    return css({
       wordBreak: 'break-all',
       wordWrap: 'break-word',
       whiteSpace: 'pre-wrap',
       lineHeight: euiTheme.font.lineHeightMultiplier,
       verticalAlign: 'top',
 
       '.euiDataGridRowCell__popover &': {
-        fontSize: euiTheme.font.scale.s,
+        fontSize,
       },
-    }),
+    });
+  },
   docViewerValueHighlighted: ({ euiTheme }: UseEuiTheme) =>
     css({
       fontWeight: euiTheme.font.weight.bold,