Various small issues with the Font Collections dialog (polishing)

Summary:

@VaibhavMalik4187 you decide whether you want those separated.

Steps to reproduce:

• open Inkscape
• open the font collection dialog

Issue 1: Renaming not possible after expanding

• Create a collection and add a font. Collapse it.
• Select a different collection and re-select the newly created one.
• Click the arrow to expand it. "I want to see which fonts are those -> Hm, the name doesn't fit"
• Click the "Rename" button at the bottom.
• Nothing happens.

Issue 2: Font names are all grey

Maybe that's supposed to indicate that they can't be edited? Looks strange.

Issue 3: Unable to apply a font from within the Font Collections dialog.

When I double-click a font, I'd expect it to be applied to the current text selection. Or there should be an apply button.

Issue 4: Dialog to confirm deletion is not very in line with Inkscape's remaining interface.

1. We usually don't ask to confirm deletion (I'm not aware of any). We delete, and then allow to undo.
2. In particular, I would not expect to be asked to confirm the deletion of an unnamed, empty font collection.
3. a question mark is missing at the end of the string in the dialog.

Issue 5: Font collections are not synchronized between windows.

When I add a font to a font collection in one window, I expect this change to propagate into the other window. Just like we do with the preferences.

Issue 6: The font dropdown is not updated when I update a font to the currently selected collection.

Instead, it is updated with the search results when I search in the font collection dialog! That's totally unexpected.

Issue 7: Reset Button is unncessary / confusing / wrong icon.

The Reset button in the font toolbar looks like "Refresh the currently selected font collection from disk". Instead, it just clears the list of selected collections altogether!

Issue 8: When dragging a font onto a collection, it collapses.

This only happens when dropping it on the collection's title. But especially for the first font in the collection, you don't have another choice.

Issue 9: Drop position indicators are misleading.

The order of the fonts inside the collection is alphabetical. That's acceptable, but in that case, the drop placement indicators are confusing. They indicate that the fonts are dropped in that specific position.

Also, dropping should not be indicated to be possible outside of a collection.

Issue 10: When creating a new font collection, all collections are collapsed.

Why?

Issue 11: When renaming a font collection, it is possible to give it the same name as an existing one.

That deletes the renamed font collection without warning. It would be better to not allow the renaming in the first place (i.e. just stay in the editing state, or revert the renaming. Both should come with a message why the renaming was not successful, probably as a popup.)

Issue 12: The font collection files are not closed properly (Windows 10).

At least, I can't delete my %appdata%/inkscape folder because those are still open, even though no Inkscape process is running anymore.

Version info

Inkscape 1.3-dev (7f8f63d10, 2023-03-28)

    GLib version:     2.76.1
    GTK version:      3.24.38
    glibmm version:   2.66.6
    gtkmm version:    3.24.7
    libxml2 version:  2.10.3
    libxslt version:  1.1.37
    Cairo version:    1.17.7
    Pango version:    1.50.14
    HarfBuzz version: 7.1.0

    OS version:       Windows 10 21H2