This removes the hard-coded binding redirects that exist within our
source tree in favor of redirects that are computed automatically. This
takes advantage of the built-in binding redirect generation support
in MSBuild. In order to get the redirects to merge properly with
the static stuff we have, I renamed the .exe.config files to App.config
which is the name the tooling looks for.

Addresses #7612.

This reverts commit 76b3818d.

This reverts commit 2ba614ea.

This reverts commit c6a1c2c8.

This reverts commit ef1f1a43.

We attempt to bind lambda args against every applicable delegate
type that could be a matching parameter, and then select the
"best" for error recovery.
This also has the effect of removing unbound lambdas from the
bound trees, replacing them with the "best" binding for error
recovery. This makes the semantic model insensitive to any further
trial bindings (i.e. mutation of the unbound lambda cache).
Fixes #12063, #11979, #11901

Remove vestigal "extensionMethodsOfSameViabilityAreAvailable"
thereby reducing coupling between internal compiler APIs.
See also #7740 #5128, where the vestigal APIs were introduced.

Our test utilities had a number of files that were duplicated in test utility projects.  Changed them to be linked files so we didn't have duplicate sources.

Fixes #12113

Make sure CompletionItems have DisplayTexts of differing lengths before determining if one is a prefix of the other.