Patterns caching (#2494)

* [patterns] A handful of mostly small changes to patterns and records:

- Clarify that patterns can call extension members. Fix #2457.
- Non-boolean results throw in relational patterns. Fix #2461.
- Maps and extractors are evaluated in source order. Fix #2466.
- Specify non-exhaustive switch errors and warnings. Fix #2474.
- Allow `final` before type annotated variables. Fix #2486.
- Rename some grammars to align with Analyzer AST names. Fix #2491.

* Add record types to the set of exhaustive types.

* Remove outdated remark.

* Fix bullet number.

* Specify how invocations are cached when checking patterns.

Fix #2107.

* Apply review feedback.

Author: munificent

accepted/future-releases/records/records-feature-specification.md

@@ -503,12 +503,12 @@ the same hash code.
 A record object has a primitive `==` operator if all of its field have primitive
 `==` operators.
 
-*Note that this is a dynamic property of a record object, not a static property
-of its type. Since primitive equality only comes into play in constants, the
+*Note that this is a dynamic property of a record object, not a property of its
+static type. Since primitive equality only comes into play in constants, the
 compiler can see the actual field values for a relevant record at compile time
 because it has the actual constant record value with all of its constant fields.
-This means records can be used in constant sets and maps keys, but only when the
-records' fields could be as well.*
+This means a record can be used in a constant set or as a constant map key, but
+only when its field values could be as well.*
 
 ### Identity