[ISO/CS C++2023] Make table headings bold

[jensmaurer]

• 5.13.3 Character literals The table header should be in bold font i.e. "Encoding prefix" "Kind" "Type" etc.
• 5.13.5 String literals The table header should be in bold font i.e. "Encoding prefix" "Kind" "Type" etc.
• 6.8.2 Fundamental types the table title should be in bold font, as should the table headers "Type" and "Minimum width". Also, please consider adding a column line between "Type" and "Minimum width".
• 6.8.3 Optional extended floating-point types Make table title bold - comment applies to all tables in this document
• 7.2.1 Value category Figure titles must be in bold - please correct throughout the document
• 25.1 General make table heading bold

[jensmaurer]

6.8.2 is mostly reject: the title and column headers are already in bold. Added a column divider line
6.8.3 reject; table titles are already bold throughout the document
7.2.1 reject; figure titles are already bold throughout the document
25.1 reject; table heading is already bold