Add solution for East Asian Width Problem

[hamano]

Is your feature request related to a problem? Please describe.

We would like to express our gratitude from the Far East for implementing the treat_east_asian_ambiguous_width_as_wide option in wezterm.
However, this option is a adhoc workaround and is inadequate.

• fullwidth for box drawing breaks the TUI screen.
• fullwidth for block elements breaks the progress bar.
• Inconsistent circled numbers width ⓪①..⑳㉑.
• Traditional Japanese charactor width does not match the Unicode recommended width.

Describe the solution you'd like

Regarding the EAW issue, better solutions:

1. Using wcswidth()
2. Set cellwidth for code points.

Since wezterm is a cross-platform application, using wcswidth() might not be appropriate.
I propose adding a cellwidth configuration option to wezterm.
This is a feature provided by mlterm, Emacs, and Vim, and it offers a practical solution to the ambiguous Unicode standard.
With this option, it is possible to unify character widths across terminal, shell, and text editors.

Based on vim's setcellwidths(), I propose the following syntax for the settings

config.cellwidths = {
  {0x2460, 0x2473, 2}, -- ①..⑳
  {0x24EA, 0x24EA, 2}, -- ⓪
  {0x2668, 0x2668, 2}, -- ♨
  {0xF113, 0xF113, 2}, -- 
}

However, it seems that keyword omission is not preferred in wezterm

config.cellwidths = {
  {first = 0x2460, last = 0x2473, width = 2}, -- ①..⑳
  {first = 0x24EA, last = 0x24EA, width = 2}, -- ⓪
  {first = 0x2668, last = 0x2668, width = 2}, -- ♨
  {first = 0xF113, last = 0xF113, width = 2}, -- 
}

I will handle the actual work and submit a pull request.
Additionally, I understand that there is a difference in perspective regarding the EAW issue between Latin users and CJK users.
If additional explanations are needed regarding the difficulties faced by the CJK users, I am more than willing to provide them.

[hamano]

ref: #1888

[NathanCummings]

Is the issue I am having in #6228 related to this do you think? Particularly look at my most recent comment where running wezterm ls-fonts --list-system shows many asian characters not being displayed properly.

[hamano]

@NathanCummings #6228 is not EAW issue.
#6228 (comment)