fix(composition): stabilize IME preedit layout for JP input (@FosterHoulston)

[FosterHoulston]

…oulston)

Description

• Limit IME composition preedit to remaining characters to prevent overflow.
• Render target glyphs during composition to avoid line shifts when kana replaces romaji.
• Tested on macOS with Safari/Firefox/Chrome using Japanese-Romaji IME; line jumps are gone.

Checks

• Adding/modifying Typescript code?

  • I have used qs, qsa or qsr instead of JQuery selectors.

• Adding quotes?

  • Make sure to include translations for the quotes in the description (or another comment) so we can verify their content.

• Adding a language?

  • Make sure to follow the languages documentation
  • Add language to packages/schemas/src/languages.ts
  • Add language to exactly one group in frontend/src/ts/constants/languages.ts
  • Add language json file to frontend/static/languages

• Adding a theme?

  • Make sure to follow the themes documentation
  • Add theme to packages/schemas/src/themes.ts
  • Add theme to frontend/src/ts/constants/themes.ts
  • Add theme css file to frontend/static/themes
  • Add some screenshots of the theme, especially with different test settings (colorful, flip colors) to your pull request

• Adding a layout?

  • Make sure to follow the layouts documentation
  • Add layout to packages/schemas/src/layouts.ts
  • Add layout json file to frontend/static/layouts

• Adding a font?

  • Make sure to follow the themes documentation
  • Add font file to frontend/static/webfonts
  • Add font to packages/schemas/src/fonts.ts
  • Add font to frontend/src/ts/constants/fonts.ts

• Check if any open issues are related to this PR; if so, be sure to tag them below.

  • Fixes Text shifting on Japanese hiragana/katakana #7256

• Make sure the PR title follows the Conventional Commits standard. (https://www.conventionalcommits.org for more info)

• Make sure to include your GitHub username prefixed with @ inside parentheses at the end of the PR title.

Closes #7256