strong mode does not check ClassTypeAlias syntax form

[jmesserly]

Strong mode does not check ClassTypeAlias syntax form.

This affects all of our checking. For example, consider this from our tests:

class A {}
class B {}

abstract class I {
    m(A a);
}

class M {
    m(B a) {}
}

class /*error:INCONSISTENT_METHOD_INHERITANCE*/T1
    extends Object with /*error:INVALID_METHOD_OVERRIDE_FROM_MIXIN*/M
    implements I {}

// BUG BUG BUG these should also have errors
class T2 = Object with M implements I;
class T3 extends T2 {}

T2/T3 produces no errors at all, unlike the (very similar) T1.

[bwilkerson]

Blocked on #29448.

[jmesserly]

@bwilkerson -- see above, this is not at all related to fields! I think maybe my description was confusing. I will remove the "originally reported at" line :)

EDIT: and I was confused at first by #27452 too :) ... until I looked into it, I didn't realize the bug was much more serious than just fields. Any time you declare a class with ClassTypeAlias syntax form, we don't check for override soundness (and a few more things). We were literally not visiting the AST node ... ooops :(. ErrorVerifier is a bit better because it was visiting the node, but I found a few checks that were missing there too.

[jmesserly]

Also BTW: I have a CL in progress :)

[jmesserly]

https://codereview.chromium.org/2837173002/