[flang] Resolve %kind and %len on intrinsic types

A `part-ref` can be `%kind` on an entity of any intrinsic type or
`%len` on a character entity. During name resolution, recognize these
and don't report an error as if they are component references.

Create symbols for these names as well as `%re` and `%im`. This is
partly for completeness so that we don't get warnings about unresolve
names. It also allows us to avoid having to do string comparisons on
these names in more than one place.

Rework `AnalyzeExpr` on structure components to make use of these
symbols and also not treat `%kind` and `%len` as derived type component
references.

Original-commit: flang-compiler/f18@65ae81ebacbe75094d7ec7d83ae3a0f35eb591d2
Reviewed-on: https://github.com/flang-compiler/f18/pull/256