Fixed contextual typing for tagged template expressions.
Removed unnecessary case; substitution expressions only occur in TemplateSpans.
Separated fourslash test to two files.
Split contextual typing test for substitution expressions into two tests.
Added tests for erroneous function expressions in both tagged/untagged template expressions.
Fixed bug where function expressions were not getting checked in template expressions.
Changed tests to error when actual contextual typing is broken.
Merge pull request #1492 from Microsoft/contextualTemplateTyping

Fixed contextual type resolution and type checking for tagged template expressions.