improvement: Only reindex workspace on onBuildTargetChanged #11488

Job	Run time
windows-latest jdk-17 unit tests 1 / 2	9m 2s
windows-latest jdk-17 unit tests 2 / 2	8m 22s
macOS-latest jdk-17 unit tests 1 / 2	10m 15s
macOS-latest jdk-17 unit tests 2 / 2	10m 12s
Gradle MacOS integration	10m 14s
ubuntu-latest jdk-17 unit tests 1 / 2	10m 19s
Sbt integration	7m 41s
ubuntu-latest jdk-17 unit tests 2 / 2	10m 13s
Maven integration	7m 35s
ubuntu-latest jdk-8 unit tests 1 / 2	10m 17s
Gradle integration	9m 5s
Scala CLI integration	10m 16s
ubuntu-latest jdk-8 unit tests 2 / 2	9m 26s
Mill integration	9m 33s
LSP integration tests	7m 45s
Scala cross tests	10m 17s
Formatting	43s
Scalafix and docs	6m 30s
Sbt-metals/scripted jdk8	1m 51s
Scala javapc tests	2m 40s
Scala3 latest NIGHTLY cross test	5m 54s
MiMa	1m 10s
	2h 49m 20s

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