The subsumption tree must treat an unconstrained type parameter as possibly null.
Also, if a previous case pattern handles all non-null input, any further case type pattern is subsumed.
Fixes #16688
Fixes #16671

Fixes #16559

Fixes #16513

Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=336030
Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=294570
Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=363714
Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=336030
Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=364165
Fixes #16296
Also adds test for #16559

Fixes #16517 

* fix EmitDefaultValue to not attempt to emit decimal constants.

* add IL verification and release verification

* added datetime test

Fixes #15910
Also fixes a sequence point issue with the let expression. Specifically, the source range for the query lambda included more than the expression of the let, but included the entire query clause. It now includes only the expression, like other query clauses.

Fixes #15934

Variables declared within a ‘for’ condition are in scope only inside the condition, incrementors and body of the loop.
Variables declared within ‘for’ incrementors are in scope only inside the incrementors.

Related to #15630.

Related to #15630.

Also add wildcards.work.md to track outstanding work.

Fixes #14825

Fixes #14636

* Implement pattern-matching in top-level scripts in which pattern variables become fields.
  Fixes #10603
* Move computation of better conversion from expression into `BetterConversionFromExpression`
* Update the out var specification to align with the implementation, and vice versa.

* Implement new syntactic disambiguation rule for pattern-matching
* Distinguish 'is' from 'as' when parsing the type
* Refactor type parsing modes to an enum.

Fixes #10492
Related to #13813

* Fix data flow analysis for using variables
Fixes #9581

* Add a requested test for cyclic inference in using statements.

fixes 7 failing pattern matching tests due to an incorrect assumption in the implementation of EnsureEnglishCulture, namely that the English culture always uses standard cultural settings; the fix now always ensures the use of the invariant culture

Fixes #13450.
Fixes #13590.

* Fix crash on "is type" operator with typeless tuple expression.

Closes #13723
Fixes #13746 

Fixes #13383

Fixes #13528.

Properly handle expression variable declared within VariableDeclaratorSyntax.ArgumentList in field declarations.

Related to #12597 and # 13417.

Related to #12597.

And other changes per code review.

Fixes #13389

Fixes #13316

Adjust scope of locals declared within a Deconstruction Declaration Statement according to the latest design.

Related to #12597.

Improve the grammar on a diagnostic.
Add further tests requested by reviewer.

Related to #12597.

Related to #12597.

Also eliminates some cases of cascaded definite assignment errors.
Fixes #13219
Fixes #13009
Fixes #12996
Fixes #10446

Related to #12597.