Initial external decorator for annotating explicit import names; Use file name as default module name in imports; Emit empty memory if there are no static segments; Update TLSF and examples accordingly

tests/parser/decorators.ts

@@ -6,5 +6,6 @@
 @unmanaged
 @sealed
 @inline
+@external("a", "b")
 @custom
 function a(): void {}

tests/parser/decorators.ts.fixture.ts

@@ -6,5 +6,6 @@
 @unmanaged
 @sealed
 @inline
+@external("a", "b")
 @custom
 function a(): void {}