Introduce new method `ConcatSourceMapBuilder::from_sourcemaps`.
Where all the sourcemaps being concatenated exist at time that you
create `ConcatSourceMapBuilder`, it's faster to use `from_sourcemaps`,
because it pre-allocates enough space for the data it will hold and so
avoids memory copying.
Before:
```rs
let mut builder = ConcatSourceMapBuilder::default();
builder.add_sourcemap(&sourcemap1, 0);
builder.add_sourcemap(&sourcemap2, 100);
builder.add_sourcemap(&sourcemap3, 100);
let combined = builder.into_sourcemap();
```
After:
```rs
let builder = ConcatSourceMapBuilder::from_sourcemaps(&[
(&sourcemap1, 0),
(&sourcemap2, 100),
(&sourcemap3, 200),
]);
let combined = builder.into_sourcemap();
```
Clone `Arc<str>`s for source text instead of creating new `Arc<str>`s and copying the string data.
For the shorter strings (names and source filenames) it's cheaper to create a new `Arc<str>` than to clone, presumably because of the overhead of atomic operations involved in `Arc::clone`.
The sourcemap implement port from
[rust-sourcemap](https://github.com/getsentry/rust-sourcemap), but has
some different with it.
- Encode sourcemap at parallel, including quote `sourceContent` and
encode token to `vlq` mappings.
- Avoid `Sourcemap` some methods overhead, like `SourceMap::tokens()`
caused extra overhead at common cases. Here using `SourceViewToken` to
instead of it.
