Merge #1638

1638: Avoid cloning a TtToken in SubtreeTokenSource::mk_token r=matklad a=lnicola

According to `perf record`, this function is the hottest one while running `ra_cli analysis-stats`:

Before:

```
6.05%  ra_cli  ra_cli        <ra_mbe::subtree_source::SubtreeTokenSource as ra_parser::TokenSource>::lookahead_nth
5.56%  ra_cli  ra_cli        <rowan::green::GreenNode as core::hash::Hash>::hash
4.16%  ra_cli  libc-2.29.so  _int_malloc
3.93%  ra_cli  ra_cli        ra_mbe::subtree_source::SubtreeTokenSource::get

Database loaded, 255 roots, 231.676882ms
Crates in this dir: 27
Total modules found: 282
Total declarations: 9642
Total functions: 3287
Total expressions: 64616
Expressions of unknown type: 9111 (14%)
Expressions of partially unknown type: 3417 (5%)
Analysis: 24.012797561s, 0b allocated 0b resident
target/release/ra_cli analysis-stats  24.60s user 0.56s system 100% cpu 25.125 total
```

After:

```
5.85%  ra_cli  ra_cli        <rowan::green::GreenNode as core::hash::Hash>::hash
4.55%  ra_cli  libc-2.29.so  _int_malloc
4.31%  ra_cli  ra_cli        ra_parser::parser::Parser::nth
3.61%  ra_cli  ra_cli        <ra_syntax::parsing::text_token_source::TextTokenSource as ra_parser::TokenSource>::lookahead_nth
3.54%  ra_cli  ra_cli        ra_syntax::syntax_node::SyntaxTreeBuilder::finish_node
3.46%  ra_cli  libc-2.29.so  _int_free
3.12%  ra_cli  libc-2.29.so  malloc
2.76%  ra_cli  ra_cli        ra_parser::event::process
2.68%  ra_cli  ra_cli        alloc::sync::Arc<T>::drop_slow
2.50%  ra_cli  ra_cli        ra_mbe::subtree_source::SubtreeTokenSource::get
2.31%  ra_cli  ra_cli        <smol_str::SmolStr as core::hash::Hash>::hash
2.04%  ra_cli  libc-2.29.so  __memmove_avx_unaligned_erms
1.92%  ra_cli  ra_cli        <ra_mbe::subtree_source::SubtreeTokenSource as ra_parser::TokenSource>::lookahead_nth

Database loaded, 255 roots, 236.176803ms
Crates in this dir: 27
Total modules found: 282
Total declarations: 9642
Total functions: 3287
Total expressions: 64620
Expressions of unknown type: 9107 (14%)
Expressions of partially unknown type: 3425 (5%)
Analysis: 22.562328486s, 0b allocated 0b resident
target/release/ra_cli analysis-stats  23.12s user 0.57s system 100% cpu 23.659 total
```

r? @edwin0cheng, @matklad 

Co-authored-by: Laurențiu Nicola <[email protected]>

0 files changed, 0 insertions, 0 deletions