feature: support italic text styling

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Support italics as a text styling option. For example:

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.31%. Comparing base (c77256e) to head (43094f8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1514      +/-   ##
==========================================
+ Coverage   41.28%   41.31%   +0.02%     
==========================================
  Files         113      113              
  Lines       17685    17692       +7     
==========================================
+ Hits         7302     7309       +7     
  Misses      10383    10383              

Flag	Coverage Δ
macos-12	36.75% <100.00%> (+0.02%)	⬆️
ubuntu-latest	43.29% <100.00%> (+0.02%)	⬆️
windows-2019	36.92% <100.00%> (+0.02%)	⬆️

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