[iOS] Improved text view injection

[Velin92]

• A default text view is always provided, to allow for easier testing and avoid using an optional, even if you should always inject it from the UI wrapper
• The initialisation is done directly by a convenience init from the text view itself
• the MentionsDisplayHelper is now managed by the viewModel which will refresh it on the textView

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[codecov-commenter]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (2f40a21) 89.96% compared to head (41f0075) 88.23%.

Files	Patch %	Lines
...WysiwygComposerView/WysiwygComposerViewModel.swift	59.25%	10 Missing and 1 partial :warning:
...ents/WysiwygComposerView/WysiwygComposerView.swift	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #935 +/- ## ========================================== - Coverage 89.96% 88.23% -1.74% ========================================== Files 32 118 +86 Lines 1565 16935 +15370 Branches 623 616 -7 ========================================== + Hits 1408 14942 +13534 - Misses 132 1964 +1832 - Partials 25 29 +4 ``` | [Flag](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/935/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | Coverage Δ | | |---|---|---| | [uitests](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/935/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `?` | | | [uitests-ios](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/935/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `?` | | | [unittests](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/935/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `88.23% <67.50%> (+13.15%)` | :arrow_up: | | [unittests-ios](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/935/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `75.70% <67.50%> (+0.62%)` | :arrow_up: | | [unittests-rust](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/935/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `89.50% <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=matrix-org#carryforward-flags-in-the-pull-request-comment) to find out more.

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