Crash introduced in 0.26.2 about char boundaries

[bugnano]

Description

When upgrading from Ratatui 0.26.1 to 0.26.2 my app started crashing when trying to display the attached file.
lorem.txt

The panic is as follows:

thread 'main' panicked at /home/fri/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ratatui-0.26.2/src/text/line.rs:477:59:
byte index 92 is not a char boundary; it is inside 'σ' (bytes 91..93) of `Μεα θε δισαθ φαλλι οφφισιις. Ναμ δυις ιριυρε αδ. Φασιλις σεθερος αλβυσιυς ατ μει, μελ υθ ρεπυδιαρε ασεντιορ ινσιδεριντ. Σαεπε πρωβατυς ηις αν`[...]

I'm displaying this file in a Table, where each line is a cell in the table.

I'll update this bug report with a minimal project that crashes.

Note that Ratatui 0.26.1 worked fine.

To Reproduce

Expected behavior

Screenshots

Environment

• OS: Linux
• Terminal Emulator: Gnome Terminal
• Font: Liberation Mono
• Crate version: 0.26.2
• Backend: Termion

Additional context

The bug was introduced by #987 .
The #987 PR doesn't take into consideration that UTF-8 uses multi-byte characters, so it's wrong to assume that

span.content[offset as usize..span_end]

is at char boundaries.
Moreover, you also must be very carful that some chars have a width of 1, some have a width of 2, and some have a width of 0, so the truncated function introduced in that PR needs to be refactored taking those things into consideration.
cc @TadoTheMiner

[EdJoPaTo]

Duplicate of #1032