Avoid duplicate generate method fixes in light bulb

Fixes #1899

Consider the following case where M1 and M2 are non-existant methods -

this.M1(System.Exception.M2());

The code fix provider for generate method was offering two fixes to generate the method M1 above. Here's why. The fix provider gets called once each for the two diagnostics on the above line - the first with span corresponding to M1 and the second with span corresponding to M2. For the first span, the fix provider correctly constructs a fix to generate M1.

For the second span the fix provider correctly realizes that it can't construct a fix to generate M2 since System.Exception is a type from metadata and not source. However, looks like fix provider has fallback code to walk up the tree and see if there are other methods that it can construct in such cases. It ends up finding the InvocationExpression for M1 up the tree and therfore ends up returning another fix for generating M1.

I didn't want to change this fall back logic since it appears to be shared across multiple GFU fix providers and I didn't want to break other legit cases where this may be required for generate method.

Instead I am fixing this by introducing equivalence key for the corresponding CodeAction to ensure that the duplicate fixes will get filtered out when the light bulb presents the list of fixes in its UI. (This is identical to equivalence keys that we have in place for other GFU fixes such as Generate Type etc.). Note that we need the equivalence key for generate method anyways to avoid duplicate fixes in other unrelated cases such as following where M is a non-existant method -

var x = this; var y = this;
string.Format("{0}:{1}", x.M(), y.M())

Also, note that in some cases where we used to offer multiple valid fixes to generate methods with the same name but different signatures before, we will now only display one fix at a time. But this is fine since user can always fix first issue then invoke light bulb again to fix 2nd issue. Example of a case where there are 2 methods with same name but different signature -

this.M(this.M());

re-filter signature help providers if the file's content type has changed

Cleaning up unused msbuild imports that was causing MSBuildWorkspace to fail

Add support for TypedConstant and TypeOf expressions

Remove use of ClearTrivia on SyntaxGenerator inputs

Re-enable the ResultProvider tests

Formatting Service should honor Smart Indent Option

...now that the CI machines have been updated.

Fixes #1178

Fix #2224 : Formatting Service should not format the whitespaces before
Braces if Smart Indentation Option is set to None

Cleaning up an unused msbuild import that was causing MSBuildWorkspace to fail. We don't have a Nuget.targets anymore

Options pages

Hide some confusing options and remove confusing words.

Use Microsoft.DiaSymReader.Native to make PDB id and stamp deterministic

Display a tooltip for hyperlinks in error list and preview pane

Display a tooltip containing url destination for hyperlinks in the error list and light bulb preview pane UIs.

Also use full fidelity (i.e. substituted)  error message in the search query in the case of hyperlinks that redirect to bing search so that we can present more relevant search results.

Fix an incorrect tautological if condition

Replace CreateStreamOnHGlobal with a custom COM Memory Stream

Fix internal bug 1138938: Keyword highlighting is unnoticeable in dark theme

The issue was that keyword highlighting was using brace highlighting tag
instead of reference highlighting tag (my guess is because brace
highlighting and keyword highlighting were written before reference
highlighting).

This change uses the reference highlighting tag. I also renamed the
keyword lighting folder structure to be called KeywordHighlighting
instead of just Highlighting.

Correctly handle simplification of Nullable{T} to T? inside crefs 

Fixes #29

Fix NullReferenceException in EE

I made a struct into a class (in 0d415c29) but I missed a null check
around an existing member access.

Emit anonymous delegates, used for dynamic, in deterministic order

Dont generate Getter/Setter when Writeonly/Readonly for VB Properties

Use a custom IStream implementation rather than the native CreateStreamOnHGlobal

Change named pipe ownership check