Add word-and-line-from-point as a mouse selection action

[warpfork]

Hello, this patch attempts to introduce a new selection mode called "word_and_line_from_point".

The behavior of this is to select the word under the cursor and then also out to the end of the line. It's functionally equivalent to using word and line_from_point in sequence and taking the combined result. (The desire for this was previously described in #6363 .)

It can be used in kitty.conf with a config line such as:

mouse_map left triplepress ungrabbed mouse_selection word_and_line_from_point

I attempted to keep the diff as minimal as possible, and here's what is included:

• MOUSE_SELECTION_WORD_AND_LINE_FROM_POINT is added to mouse selection types in C and python bindings, so it's communicable from the config options layer.
• the string "line_from_word" is mapped to MOUSE_SELECTION_WORD_AND_LINE_FROM_POINT in kitty/options/utils.py function, so that string can be recognized in the config file.
• in mouse.c, mouse_selection function gains a new case so it can forward the MOUSE_SELECTION_WORD_AND_LINE_FROM_POINT action to the screen_selection_* functions.
• EXTEND_WORD_AND_LINE_FROM_POINT is added to the SelectionExtendModes enum in C, so our mode can be communicated to the screen_*_selection functions.
• screen_update_selection gains a very small branch for EXTEND_WORD_AND_LINE_FROM_POINT in the middle of the overall EXTEND_LINE logic, which performs the search for word. If there's a word, the selection start moves to the start of the word. (If there's no word, the selection is made as it would be otherwise by regular EXTEND_LINE, meaning it starts at the cursor.)
• documentation added in kitty/options/definition.py.

I'm testing this manually and it seems to have the desired behavior. It works on normal lines; it works on long lines that wrapped; it works on the non-first rendered line of wrapped lines; it combines fine with extending selections. I've been driving it around for a few days now and encountered no surprising behavior.

I'm happy to accept any feedback about the feature name, or the code. I think it works, and I tried to keep the change minimal. But this is my first attempt to submit a patch to Kitty, and also the first time I've touched C code in many years, so I cannot guarantee it is perfect on the first pass. :) Thank you very much for your review!

[kovidgoyal]

At a quick glance it looks fine. Some comments:

1. Add some docs to options/definition.py -- wherever line_from_point is used to its docs add a sentence saying that one can instead use word_and_line_from_point to have it select the word under the cursor and extend to end of line

2. rename line_from_word to something like word_and_line_from_point

I'll review in detail after you make these changes.

[warpfork]

That's a much better name, thanks. Rebased to that.

Brief docs also added to definition.py.

[warpfork]

🎉 🤩 💃 Thank you!! This made my day.