Refactor MergeKeyboardInfo

Refactor MergeKeyboardInfo to handle these keyboard scenarios:

* JS file not in package (web only)
* KMP package with kmx files (desktop only)
* KMP package with JS files (mobile only)
* KMP package with kmx and JS files (desktop, android, ios)

## Changes ##
* Rename `FKMXFiles` to `FPackageKMXFileInfos`
* Create private var `FPackageJSFileInfos`
* Update `TMergeKeyboardInfo.LoadKMPFile` to populate `FPackageJSFileInfos`
* Rename `FJSFiles` to `FJSFileInfo`, change it from array to scalar, and apply only to js files outside package
* Update `LoadKMPFile` to use the Keyboards structure in `FKMPInfFile` to determine which files inside the package are keyboards (`FKMPInfFile.Keyboards`)
* Rename `CheckKMXFilenames` to `CheckPackageKetyboardFilenames` and update to report on .js and .kmx file inside the .kmp
* Update `kmxfile.GetKeyboardInfo` to read targets store and persist in KeyboardInfo
* Update `AddPlatformSupport` to account for targets