[SDK] Add missing return type in RoomApi.sendStateEvent()

[mnaturel]

Type of change

• Feature
• Bugfix
• Technical
• Other : Enhancement

Content

Returning the id of the newly created state event in methods to send state events.

Motivation and context

Closes #5855
For instance, In some situation it may be useful to know the id of the newly created event to attach other related events to it.

Screenshots / GIFs

Tests

• Change the name of a room
• Check you see log of the creation of the state event.

Tested devices

• Physical
• Emulator
• OS version(s): Android 11

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/vector-im/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/vector-im/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[bmarty]

LGTM!

[github-actions]

Unit Test Results

122 files  122 suites   2m 2s ⏱️
205 tests 205 ✔️ 0 💤 0 ❌
690 runs  690 ✔️ 0 💤 0 ❌

Results for commit 3b022ee.