This reverts commit c6a1c2c8.

* Test ExportedType table content

* Refactoring of code emitting exported types

* Remove MetadataWriter.GetExportedTypeFlags

* add vb version 15

* Fix case on LanguageVersion

* Tests: fix minasync Task<T> to derive from Task

* Tests: provide MinAsyncCorlibRef

This combines the async features of minasync with mincorlib to produce
a minimum unversioned corlib with async stubs.

* Compilation: use System.Object from target corlib

When creating a script compilation without an explicit return type,
System.Object was being resolved via reflection from the host.

This resulted in an implicit dependency of a script compilation on the
host corlib, even if a different corlib was specified as a reference
for the compilation (e.g. Xamarin.iOS).

Fix this by using System.Object as defined in the corlib resovled
for the compilation.

* Tests: fix minasync Task<T> to derive from Task

* Tests: provide MinAsyncCorlibRef

This combines the async features of minasync with mincorlib to produce
a minimum unversioned corlib with async stubs.

* Compilation: use System.Object from target corlib

When creating a script compilation without an explicit return type,
System.Object was being resolved via reflection from the host.

This resulted in an implicit dependency of a script compilation on the
host corlib, even if a different corlib was specified as a reference
for the compilation (e.g. Xamarin.iOS).

Fix this by using System.Object as defined in the corlib resovled
for the compilation.

Expression trees can naturally ignore return value when necessary and old compiler was skipping relaxation in this case.

Fixes: #8804

* Bug 217740: Repro and test harness for C#

* Testing and fixing loading scenario in C# and VB

* Verifying VB case using attribute on field

* Adding more tests

* Adding VB tests

* Adding tests

* More tests on fields with double-attributes

* New test constraint

* Fixing VB side to new test constraints

* Fixing C# side to new test constraints

* Fixing remaining tests

* Adding comments

* Fixing VB field scenario too

Do not report warnings for malformed InformationalVersionAttribute values

Adjust implementation of MemberSemanticModel.GetEnclosingBinderInternal to avoid NullReferenceException.

The change addresses the situation when SemanticModel is created to speculate on a With block and the function is trying to locate a binder for the With expression within the block.

Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=187910&_a=edit.

Restore backward compatibility in the way conversion from a reference type to an intrinsic value type is evaluated.

Fixes #9887.