Removed lookup of TemplateStringsArray for non-ES6 targets.

This will enable custom ES3/ES5 lib.d.ts files that omit the TemplateStringsArray type, but don't need it anyway.
Baselines, using 'unknown' as a default type.
Fixes to type guards
Fixed issue in harness where lib.d.ts errors are note counted.
Added tests for defining TemplateStringsArray in certain contexts.
Merge branch 'master' into typeGuards
Modifying tests and accepting new baselines
Merge pull request #1160 from Microsoft/weDontNeedNoTemplateStringsArrayPreEs6

Default to 'unknown' for the template strings array type in pre-ES6 targets.
Addressing CR feedback
formatting: handle templates spans
Merge pull request #1163 from Microsoft/typeGuards

Fixes to type guards
added more tests
Function and constructor types in the syntax tree.
Merge pull request #1167 from Microsoft/formatting_templates

formatting: handle templates spans
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