Add menu and context item icons and update libcosmic.

[edfloreshz]

This pull request updates libcosmic to its latest version, this includes new features and improvements to the application, including the addition of an "About" section, various updates to the context drawer functionality and menu item icons.

Summary:

• Added an "About" section to the application, including details such as the name, author, version, license, and links to the repository and support.
• Introduced an icon cache to manage and optimize the use of icons throughout the application.

Context Drawer Enhancements:

• Updated the context drawer to use a new context_drawer module, simplifying the way context pages are displayed and managed.

Codebase Updates:

• Included new icons for various actions in the application menu.
• Updated the Cargo.toml file to include the "about" feature.

Localization:

• Added new localization entries for the "About" section.

[git-f0x]

This likely needs UX approval.
But unrelated to that, the header menu width should possibly be increased slightly (since it isn't dynamic yet), since e.g. Show hidden files is very close to its shortcut.
Edit: Also, the about widget shouldn't be added yet, since the target Rust version is 1.80 (see #658).

[edfloreshz]

I can remove the about feature, no problem.

[jackpot51]

I am converting to a draft until we decide on this. The icons will need to be source from the cosmic icon theme, at least.

[edfloreshz]

Sure, I'll wait until we hear from Maria to switch the icons.