[Android + Rust] Several editor fixes and tweaks

[jmartinesp]

Changes in this PR:

Android

• Fix incorrect transformation of NBSP chars to 'extra char' spans to indicate offsets between the RTE state and the EditText.
• Add undo/redo context menu actions, also add them to Ctrl+Z and Ctrl+Shift+Z keyboard shortcuts (which is what some software keyboards use).
• Make sure we don't try to apply spans outside the bounds of the parsed text.
• Make sure applying a selection only happens inside the actual bounds of the Editable object.
• Destroy the ComposerModel when it crashes and we instantiate a new one. It should remove a source of memory leaks.

Rust

• Fix for replacing text/deleting several selected empty paragraphs. Previously, any text in them was removed but the actual paragraphs were kept.
• After replacing text, make sure the new selection is inside the bounds of the DOM tree.

Tests

If you want to run manual tests, to double check the changes:

• Open either the Android app with these changes or build the example-compose project.
• Write a text with several empty paragraphs (consecutive line breaks). The select all and delete it. The editor should be blank.
• Paste some text with some NBSP characters, try editing text after these characters. If it doesn't crash or behaves strangely, it's working properly.

The rest of the changes are for issues that we don't really know how to reproduce, but we know are present.

[codecov-commenter]

Codecov Report

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

Comparison is base (532b1df) 87.38% compared to head (3fc6833) 89.50%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #916 +/- ## ============================================ + Coverage 87.38% 89.50% +2.12% ============================================ Files 167 86 -81 Lines 19030 15371 -3659 Branches 1037 0 -1037 ============================================ - Hits 16629 13758 -2871 + Misses 2096 1613 -483 + Partials 305 0 -305 ``` | [Flag](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/916/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/916/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `?` | | | [uitests-android](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/916/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/916/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/916/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `89.50% <100.00%> (+4.00%)` | :arrow_up: | | [unittests-android](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/916/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `?` | | | [unittests-ios](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/916/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `?` | | | [unittests-rust](https://app.codecov.io/gh/matrix-org/matrix-rich-text-editor/pull/916/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=matrix-org) | `89.50% <100.00%> (+0.07%)` | :arrow_up: | 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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[sonarcloud[bot]]

Quality Gate passed

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