This commit introduces the Unicode placeholder image placement method.
In particular:
- Virtual placements can be created by passing `U=1` in a put command.
- Images with virtual placements can be displayed using the placeholder
character `U+10EEEE` with diacritics indicating rows and columns.
- The image ID is indicated by the foreground color of the placeholder.
Additionally, the most significant byte of the ID can be specified via
the third diacritic.
- Underline color can be optionally used to specify the placement ID.
- A bug was fixed, which caused incomplete image removal when it was
overwritten by another image with the same ID.
This allows us to have newline not affect the wrap status of a line.
Now a lines wrapping status is changed only when the last cell
in the line is changed. This actually matches the behavior of many other
terminal emulators so is probably a good thing from a ecosystem
compatibility perspective.
The fish shell expects this weird behavior of newline not changing
wrapping status, for unknown reasons, which is the actual motivation for
doing all this work.
Fixes#5766
Without this, Clang would complain:
```
In file included from kitty/fonts.c:9:
In file included from kitty/fonts.h:9:
kitty/lineops.h:67:29: error: suggest braces around initialization of subobject
[-Werror,-Wmissing-braces]
const CellAttrs zero = {0};
^
{}
```
This ensures that there is no leftover line when the shell redraws the prompt,
by making the prompt a simple single character prompt before rewrapping.
Needed for output of hyperlinks, also more efficient, since avoids
malloc per line. Also fix pagerhist not having SGR reset at the start of
every line.
Split up the Cell structure into a CPUCell and a GPUCell. Only the
GPUCell part needs to be sent to the GPU. Should make kitty use even
less system resources and make a performance difference on systems where
the GPU bandwidth is constrained.
Also allows adding more CPU only data in the future without affecting
GPU bandwidth. For example, hyperlinks or more combining characters.
