8280: Borrow text of immutable syntax node r=iDawer a=iDawer
In https://github.com/rust-analyzer/rowan/pull/101 `rowan::SyntaxNode::green` returns `Cow<'_, GreenNodeData>`. It returns borrow of green node of immutable syntax tree node.
Using this we can return borrowed text from `ast::Name::text`.
~~However now it allocates in case of mutable syntax trees.~~ (see next comment)
The idea comes from https://github.com/rust-analyzer/rowan/pull/100#issuecomment-809330325
Co-authored-by: Dawer <7803845+iDawer@users.noreply.github.com>
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