Scala full changelog

Highlights of the release:
Support records in JavaParsers
Port JVM backend refactor from Scala 2

Highlights of the release:
Make truncation by characters in REPL configurable #16167
New (experimental for now) lazy vals implementation #15296
Make coverage instrumentation more robust
Resolve overloading: keep track of prefix and indices of all default getters
Let accessors inherit @experimental annotations from accessed symbols

Highlights:
TASTy Reader support for Scala 3.0.0 (#9617 by @bishabosha)
The splain compiler plugin by @tek was integrated into the compiler, available with the -Vimplicits and -Vtype-diffs flags (#7785)
Escaped double quotes now work as expected in string interpolations, both s""" and s"$"" (#8830 by @eed3si9n and #9536 by @martijnhoekstra)
Other Changes:
Optimized BigInt implementation (#9628) by @denisrosset
Support JDK15 text blocks in Java parser (#9548) by @harpocrates
Stricter override checking for protected Scala members which override Java members (#9525) by @kynthus
Check private[this] members in override checking (#9542)
More accurate outer checks in patterns (#9504)
Allow renaming imports from _root_ (#9482) by @som-snytt
Make more annotations extend ConstantAnnotation (9336) by @BalmungSan
A number of syntax changes were added to simplify cross-building between Scala 2 and 3
Don't error (only warn) on symbol literals under -Xsource:3 (#9602)

Highlights:
TASTy reader: add support for Scala 3.0.0-RC1
Allow name-based extractors to be irrefutable
JDK 16 and 17 support in the optimizer

This release has:
A brand-new Vector implementation
Configurable warnings

This is primarily a bug fix release that fixes several regressions in 2.13.0.

Release summary:
2.13 improves Scala in the following areas:
Collections: Standard library collections have been overhauled for simplicity, performance, and safety. This is the centerpiece of the release.
Standard library: Future is faster and more robust. Elsewhere, useful classes and methods have been added.
Language: Literal types, partial unification, by-name implicits, more.
Compiler: 5-10% faster, deterministic output, improved optimizer.
Collections redesign:
Standard library collections have been overhauled for for simplicity, performance, and safety.
This is the centerpiece of the release.
Most ordinary code that used the old collections will continue to work as-is, except as detailed below.