Improve screenshot testing with ComposablePreviewScanner (#3125)

* Use ComposablePreviewScanner to rework how screenshot testing works
* Add test sharding
* Update screenshots
* Fixes for Element Gallery

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Co-authored-by: ElementBot <benoitm+elementbot@element.io>
Co-authored-by: Benoit Marty <benoit@matrix.org>

libraries/roomselect/impl/build.gradle.kts

@@ -17,7 +17,6 @@
 plugins {
     id("io.element.android-compose-library")
     alias(libs.plugins.anvil)
-    alias(libs.plugins.ksp)
     id("kotlin-parcelize")
 }
 
@@ -40,7 +39,6 @@ dependencies {
     implementation(projects.libraries.designsystem)
     implementation(projects.libraries.uiStrings)
     api(projects.libraries.roomselect.api)
-    ksp(libs.showkase.processor)
 
     testImplementation(libs.test.junit)
     testImplementation(libs.coroutines.test)