Tweaks for Excel to Markdown conversion

[cebtenzzre]

There are a few changes here that we didn't have time to discuss in the previous PR:

• _Underlines_ seem to be recognized by Llama 3, so use them
• Not all spreadsheets use the first row as a header. Llama 3 seems to generalize better with no header row.
• Empty cells seem to not be well supported by Llama 3 unless there is a space in them (this matters more for spreadsheets with lots of horizontal whitespace)
• Long filenames were exceeding the width and height of the attached file cards. Probably we should be using a RowLayout and not a Row so it's easier to automatically constrain the width of the elements, but this change works too.

Needs a changelog entry once we decide which of these changes to keep.

Follow-up to #3007

[manyoso]

The only one I'm worried about is the extra spaces. This increases context length of the document so I'd like to see a test cast this fixes...

[manyoso]

This markdown is not displayable by QTextDocument apparently as a markdown table. The issue seems to be the missing headers.

Moreover, this is the raw markdown you're producing in your test case:

|---|---|---|---|---|---|---|---|
|||||||||
|The password is not:|||Formula 1:|Formula 2:||||
|Apples|||4|6||||
|||||||||
|||||||||
||||**Bold**|||||
||||_Underline_|||||
|The password is not:|||*Italics*|||||
|Pears|||***Bold Italics***|||||
||||||||The password is:|
||||||||Stairs|

Which apparently doesn't have the spaces you intended to add?

[manyoso]

This seems to cause problems and I don't think it is actually helping with the password test case as the resulting markdown doesn't have extra spaces.

[manyoso]

The escaping is worse. I am getting this kind of md on the walt disney xlsx example for produced markdown:

| | | | | | | |
|---|---|---|---|---|---|---|
|~~***_Walt Disney Co\\1_***~~| | | | | | |
|~~***_Consolidated Income Statement_***~~| | | | | | |
| | | | | | | |
|US$ in millions| | | | | | |
|~~***_12 months ended:_***~~|~~***_45199_***~~|~~***_44835_***~~|~~***_44471_***~~|~~***_44107_***~~|~~***_43736_***~~|~~***_43372_***~~|
|Services|79562\\10|74200\\10|61768\\10|59265\\10|60542\\10|50869\\10|
|Products|9336\\10|8522\\10|5650\\10|6123\\10|9028\\10|8565\\10|
|~~***_Revenues_***~~|~~***_88898\\10_***~~|~~***_82722\\10_***~~|~~***_67418\\10_***~~|~~***_65388\\10_***~~|~~***_69570\\10_***~~|~~***_59434\\10_***~~|
|Cost of services\\1 exclusive of depreciation and amortization|\\153139\\10|\\148962\\10|\\141129\\10|\\139406\\10|\\136450\\10|\\127528\\10|

Which looks like this:

[manyoso]

Notice the strikeout as well...

[cebtenzzre]

There was a mistake in my regex and a bug in QXlsx. I have fixed both of them.