Highlights:
* Performance improvements in the ollections
library: algorithmic improvements and
changes to avoid unnecessary allocations.
* Performance improvements in the compiler.
* ASM was upgraded to 7.3.1, allowing the
optimizer to run on JDK 13+.
Full release notes: https://github.com/scala/scala/releases/tag/v2.12.11
Reviewers: Manikumar Reddy <manikumar.reddy@gmail.com>, Chia-Ping Tsai <chia7712@gmail.com>