Incorrect handling of character width for half-width katakana

[elfham]

Description

There seems to be something wrong with the way the character width of half-width katakana is handled.

Steps to Reproduce

Environment:

irb(main):001:0> irb_info
=>
Ruby version: 2.7.5
IRB version: irb 1.3.8.pre.11 (2021-10-09)
InputMethod: ReidlineInputMethod with Reline 0.2.8.pre.11
RUBY_PLATFORM: amd64-freebsd13
LANG env: ja_JP.UTF-8
East Asian Ambiguous Width: 2

Scenario:

In irb, type "ｶﾞｷﾞｸﾞｹﾞｺﾞ

Expected:

% irb
irb(main):001:0" "ｶﾞｷﾞｸﾞｹﾞｺﾞ
                            _

The cursor is located at the end of line.

Actual:

% irb
irb(main):001:0" "ｶﾞｷﾞｸﾞｹﾞｺﾞ
                       _

The cursor is located in the word.

irb(main):001:0> ga = "ｶﾞ"
=> "ｶﾞ"
irb(main):002:0> ga.grapheme_clusters
=> ["ｶﾞ"]
irb(main):003:0> Reline::Unicode.get_mbchar_width(ga)
=> 1
irb(main):004:0>

Terminal Emulator

PuTTYrv 0.76-ranvis (CJK)