Split XML gen action should have different mnemonic

[sluongng]

Description of the feature request:

It should not use the same TestRunner mnemonic, which is very confusing for newer users.

It would be best to have a separate execution group for this as well so that when running on RBE, users can use a different set of exec properties for this action (i.e. when running bazel coverage, the default exec properties of TestRunner action may not include gcov, while the split gen xml action does require gcov installed to run successfully.)

Which category does this issue belong to?

No response

What underlying problem are you trying to solve with this feature?

Making it easier for Build Event UI users to tell split xml gen action apart from TestRunner actions.

Also make coverage a bit easier to configure.

Which operating system are you running Bazel on?

No response

What is the output of bazel info release?

No response

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

Should still be relevant as of Bazel 9

What's the output of git remote get-url origin; git rev-parse HEAD ?

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

Probably need to start here

bazel/src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java

Lines 473 to 485 in 156c627

	return new SimpleSpawn(
	action,
	args,
	envBuilder.buildOrThrow(),
	// Pass the execution info of the action which is identical to the supported tags set on the
	// test target. In particular, this does not set the test timeout on the spawn.
	action.getExecutionInfo(),
	/* inputs= */ NestedSetBuilder.create(
	Order.STABLE_ORDER, action.getTestXmlGeneratorScript(), action.getTestLog()),
	/* tools= */ NestedSetBuilder.emptySet(Order.STABLE_ORDER),
	/* outputs= */ ImmutableSet.of(action.getTestXml()),
	/* mandatoryOutputs= */ null,
	SpawnAction.DEFAULT_RESOURCE_SET);

and make sure we use a new action instead of the parent TestRunner action to create the spawn?