style: Update to Material Symbol

[AndyScherzinger]

Replace all app icon work with Material Symbol version in alignment with @jancborchardt

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 23.60%. Comparing base (75445bd) to head (5ef3463). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6054 +/- ## ========================================= Coverage 23.60% 23.60% Complexity 457 457 ========================================= Files 246 246 Lines 11716 11716 Branches 2150 2151 +1 ========================================= Hits 2766 2766 Misses 8635 8635 Partials 315 315 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/6054/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | Coverage Δ | | |---|---|---| | [javascript](https://app.codecov.io/gh/nextcloud/calendar/pull/6054/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.18% <ø> (ø)` | | | [php](https://app.codecov.io/gh/nextcloud/calendar/pull/6054/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `58.65% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud#carryforward-flags-in-the-pull-request-comment) to find out more.

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[AndyScherzinger]

@miaulalala any hints on how to get the checks from red to green? 🙏

[miaulalala]

Let's see if a rebase does it

[AndyScherzinger]

@miaulalala nope, cause any other recent PR fails on the same checks, i.e. #6056