Stop watching hierarchies during the build when reaching the maximum number of watched directories

[wolfs]

After #14101, we stop watching hierarchies at the end of the build when the maximum of watched hierarchies has been reached. We should already stop watching hierarchies during the build when changes from the VFS come in and we reach the limit.

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cc: @gradle/execution

[stale]

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[lptr]

This hasn't been a source of problems for some time, let's reopen if it becomes one.