I noticed my error messages while testing were names like `"E:\Github\compiler\binder.ts"` - with this change, they originate from the correct location (are are thus clickable links in the console). The previous path may have been required as a workaround for some old version of the tools we use, but is apparently no longer needed.
* 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* Remove outdated comments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
1. convertToArray is a duplicate of arrayFrom
2. inferFromParameterTypes delegates immediately to inferFromTypes
3. One usage of arrayFrom instantiated a whole iterator only to take the
first element, which is the same as calling `next`.
The code fix for spelling correction needs to provide suggestions based
on the apparent type since sometimes the type at a location will be a type
parameter. One such example is `this`.
Fixes#16744
