The errors produced when error were encountered while interpreting the
content of a directive was often incomprehencible. With this change
these kind of error messages should be easier to understand and diagnose.
PR Close#20459
Removes the tsickle dependency added when tsickle was added to the
transform compiler.
Added a test to ensure stray dependencies are not added and no
errors are introduced during module flattening.
Reworked some of the code so asserts are no longer necessary.
Added additional and potentially redundant checks
Added checks where the null checker found real problems.
PR Close#16422
