This is a step towards introducing a borrowed RepoPath type. The current
RepoPath type is inefficient as each component String is usually short. We
could apply short-string optimization, but still each inlined component would
consume 24 bytes just for e.g. "src", and increase the chance of random memory
access. If the owned RepoPath type is backed by String, we can implement cheap
cast from &str to borrowed &RepoPath type.
Many of the `TreeBuilder` users have an `Option<TreeValue>` and call
either `set()` or `remove()` or the builder depending on whether the
value is present. Let's centralize this logic in a new
`TreeBuilder::set_or_remove()`.
Suppose many override entries share the same parent directories, it should
be cheaper to look up the tree_cache from leaf than root. I also think
recursion is easier to follow than for loop.
Let's acknowledge everyone's contributions by replacing "Google LLC"
in the copyright header by "The Jujutsu Authors". If I understand
correctly, it won't have any legal effect, but maybe it still helps
reduce concerns from contributors (though I haven't heard any
concerns).
Google employees can read about Google's policy at
go/releasing/contributions#copyright.
