Simplifier does not preserve trivia for a bunch of simplifications

[shyamnamboodiripad]

#50 reports one case where the simplifier doesn't preserve trivia. This case is addressed in PR #1965. However, there are several other cases where simplifier doesn't preserve trivia today -

• System.\* comment *\ Int32 -> int (i.e. simplify to predefined type in both member access as well as qualified names)
• System. \* comment *\ Int32 -> alias (i.e. simplify to alias both in both member access as well as qualified names)
• Nullable< \*comment *\ T> -> T?
• Preserving trivia when replacing generic names with aliases
• Removing type arguments for generic methods
• Simplifying alias qualified names global::System...

Logging this issue so that we can -

• Audit all the parts of the simplifier that need fixing (in addition to the above list, I am also not sure whether we preserve trivia correctly in other reducers such as extension method simplification, parenthesis simplification etc. some of which can only be invoked via API) and
• Test all the changes properly