Reland "Avoid computing the URI scanner tables at runtime."

This is a reland of commit 5875a9b

Original change's description:
> Avoid computing the URI scanner tables at runtime.
>
> Precompute the table and store it as a String literal.
>
> Fixes #49108.
>
> Bug: https://dartbug.com/49108
> Change-Id: I33d3e768ad2013ad2edec3558fcd3da39b3f4f32
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/247383
> Reviewed-by: Slava Egorov <[email protected]>
> Commit-Queue: Lasse Nielsen <[email protected]>
> Auto-Submit: Lasse Nielsen <[email protected]>

Bug: https://dartbug.com/49108
Change-Id: Ia2c19457a10708b03817e8da4bd6d9dec35c012a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/247961
Reviewed-by: Martin Kustermann <[email protected]>
Reviewed-by: Stephen Adams <[email protected]>
Commit-Queue: Lasse Nielsen <[email protected]>

Author: lrhn