* Created a branded type for escaped strings
Then flowed it throughout the compiler, finding and fixing a handful of
bugs relating to underscore-prefixed identifiers in the process.
Includes a test for two cases noticed - diagnostics from conflicting
symbols from export *'s, and enum with underscore prefixed member emit.
* Correctly double underscores WRT mapped types
* Add fourslash tests for other fixed issues
* use function call over cast
* Update forEachEntry type accuracy
* Just use escaped names for ActiveLabel
* Remove casts from getPropertyNameForPropertyNameNode
* This pattern has occurred a few times, could use a helper function.
* Remove duplicated helper
* Remove unneeded check, use helper
* Identifiers list is no longer escaped strings
* Extract repeated string-getting code into helper
* Rename type and associated functions
* Make getName() return UnderscoreEscapedString, add getUnescapedName()
* Add list of internal symbol names to escaped string type to cut back on casting
* Remove outdated comments
* Reassign interned values to nodes, just in case
* Swap to string enum
* Add deprecated aliases to escapeIdentifier and unescapeIdentifier
* Add temp var
* Remove unsafe casts
* Rename escaped string type as per @sandersn's suggestion, fix string enum usages
* Reorganize double underscore tests
* Remove jfreeman from TODO
* Remove unneeded parenthesis
Make Program.getMissingFilePaths required
Assume getMissingFilePaths always returns a defined value
Make getMissingFilePaths internal
Replace nullable-bool with enum
Update type to reflect possibility of undefined
Use deepEqual to simplify tests
Make condition const
Don't bother cleaning up map before freeing it
Switch from foreach to for-of to simplify debugging
Use a Map, rather than a FileMap, to track open FileWatchers
Fix compilation errors
Introduce and consume arrayToSet
Fix lint warnings about misplaced braces
Delete incorrect comment
Delete from map during iteration
Eliminate unnecessary type annotations
1. Expose missing files from the `Program`.
2. In `tsc --watch` and `tsserver`, add file watchers to missing files.
3. When missing files are created, schedule compilation (tsc) or refresh
the containing projects (tsserver).
* importFixes: Support missing "React" at a JSXOpeningElement
* Fix nextLineRule linting
* Rename to resolveJsxNamespaceAtLocation
* Expose getJsxNamespace and resolveNameAtLocation separately
