Expose simple names on a missing types's synthetic declaration

[danysantiago]

In javac, an ErrorType is a DeclaredType and one can get an Element out of it. Its simpleName will be the name as it was defined in the sources.

But in KSP, the KSDeclaration of a an error KSType is a synthetic declaration (specifically that KSErrorTypeClassDeclaration singleton) and its simple name is always <Error>.

This would be very helpful for reporting to the user nice traces to the missing type:

package test

import bar.MissingType;

class TestClass {
  fun foo(missing: MissingType) = TODO()
}

Validation trace:
    => element (CLASS): test.TestClass
    => element (METHOD): foo(MissingType)
    => type (EXECUTABLE method): (MissingType)void
    => type (ERROR parameter type): MissingType

Note that if the type is qualified in the source, it will be similarly be reported as its 'simple name' in javac:

 fun foo(missing: bar.MissingType) = TODO()

    => type (ERROR parameter type): bar.MissingType

[kuanyingchou]

EDIT: Just found that it's already mentioned above. Please ignore this.

Just to add that javac/kapt keeps the original referenced names and not just simple names, for example, with:

class Foo {
    fun barQualified(missing: bar.MissingType) = TODO()
}

We can get "bar.MissingType" in javac/kapt.