Add iCalendar Language

[DecimalTurn]

Description

I'm adding iCalendar as a data format.
This PR closes #6910

PS: This is a duplicate of #6911. I wanted to rename the branch associated with that PR, but apparently this closes the PR. Sorry for the inconvenience.

Checklist:

• I am adding a new language.

  • The extension of the new language is used in hundreds of repositories on github.com.

    • Search results for each extension:
      • ics: https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.ics+BEGIN
      • ical: https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.ical+BEGIN

  • I have included a real-world usage sample for all extensions added in this PR:

    • https://raw.githubusercontent.com/NateScarlet/holiday-cn/master/2024.ics
      • License: MIT
    • https://raw.githubusercontent.com/KDE/kcalutils/22e829cdc9d1301485f29c9e125d557b2269b8b1/autotests/data/todo-2.ical
      • License: CC0

  • I have included a syntax highlighting grammar: https://github.com/kimsey0/iCalendar-sublime

  • I have added a color

    • Hex value: #ec564c
    • Rationale: Same color as the logo for the Apple Calendar app

  • [ ] I have updated the heuristics to distinguish my language from others using the same extension. (Unused extensions)

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.