Fix issue with case sensitivity of noUnusedVariable rule on Windows (#2819)
Fix issue with case sensitivity of noUnusedVariable rule on Windows (#2819)

When TSLint is being used to provide as-you-type linting as in Angular
IDE, incorrect configuration of program created in
makeUnusedCheckedProgram function is causing whole functionality to blow
up. The core of the issue is that SourceFiles are being assigned case
sensitive path when program is recreated for TSLint validation, which
later causes that wrong path to stick and file not found problems appear
in whole IDE.
palantir/tslint,IllusionMH/tslint,andy-ms/tslint,andy-ms/tslint,andy-ms/tslint,berickson1/tslint,andy-hanson/tslint,andy-hanson/tslint,berickson1/tslint,JoshuaKGoldberg/tslint,mprobst/tslint,palantir/tslint,JoshuaKGoldberg/tslint,mprobst/tslint,IllusionMH/tslint,palantir/tslint,JoshuaKGoldberg/tslint,berickson1/tslint,andy-hanson/tslint,mprobst/tslint,IllusionMH/tslint