This step converts as many explicit accesses as possible in favor of direct imports from the modules in which things were declared. This restores the code (as much as possible) back to how it looked originally before the explicitify step, e.g. instead of "ts.Node" and "ts.Symbol", we have just "Node" and "Symbol".
This step converts each file into an exported module by hoisting the namespace bodies into the global scope and transferring internal markers down onto declarations as needed.
The namespaces are reconstructed as "barrel"-style modules, which are identical to the old namespace objects in structure. These reconstructed namespaces are then imported in the newly module-ified files, making existing expressions like "ts." valid.
* Enable '--strictNullChecks'
* Fix API baselines
* Make sys.getEnvironmentVariable non-nullable
* make properties optional instead of using `| undefined` in thier type
* reportDiagnostics should be required
* Declare firstAccessor as non-nullable
* Make `some` a type guard
* Fix `getEnvironmentVariable` definition in tests
* Pretend transformFlags are always defined
* Fix one more use of sys.getEnvironmentVariable
* `requiredResponse` accepts undefined, remove assertions
* Mark optional properties as optional instead of using `| undefined`
* Mark optional properties as optional instead of using ` | undefined`
* Remove unnecessary null assertions
* Put the bang on the declaration instead of every use
* Make `createMapFromTemplate` require a parameter
* Mark `EmitResult.emittedFiles` and `EmitResult.sourceMaps` as optional
* Plumb through undefined in emitLsit and EmitExpressionList
* `ElementAccessExpression.argumentExpression` can not be `undefined`
* Add overloads for `writeTokenText`
* Make `shouldWriteSeparatingLineTerminator` argument non-nullable
* Make `synthesizedNodeStartsOnNewLine` argument required
* `PropertyAssignment.initializer` cannot be undefined
* Use one `!` at declaration site instead of on every use site
* Capture host in a constant and avoid null assertions
* Remove few more unused assertions
* Update baselines
* Use parameter defaults
* Update baselines
* Fix lint
* Make Symbol#valueDeclaration and Symbol#declarations non-optional to reduce assertions
* Make Node#symbol and Type#symbol non-optional to reduce assertions
* Make `flags` non-nullable to reduce assertions
* Convert some asserts to type guards
* Make `isNonLocalAlias` a type guard
* Add overload for `getSymbolOfNode` for `Declaration`
* Some more `getSymbolOfNode` changes
* Push undefined suppression into `typeToTypeNodeHelper`
* `NodeBuilderContext.tracker` is never `undefined`
* use `Debug.assertDefined`
* Remove unnecessary tag
* Mark `LiteralType.freshType` and `LiteralTupe.regularType` as required
* Add telemetry for open JS files
* Send event every time
* Keep stats even for closed files
* Remove tsCheckCountForOpenFilesTelemetry
* Use 'info.path'
* Update API
* Add support for per-file jsx pragmas
* Add error for using jsx factory pragma with fragments
* More tests, use different regex class for pragma capture
* Unify all pragma parsing machinery
* Don't count a write-only reference as a use
* Split isWriteAccess to isWriteOnlyAccess and isReadOnlyAccess
* Update "unusedParameterUsedInTypeOf" to use "b"
* Update diagnostic messages: "is never used" -> "its value is never read"
* Use a WriteKind enum
* Rename enum and move documentation to enum members
