Resolve bits/union nested type naming

Resolve bits/union nested type naming

The cases where we allocate an enumeration, bits or union type
for a leaf-like construct (leaf, leaf-list) need to handle an
edge case -- JLS does not allow nested classes to be named the
same as the enclosing class.

Enumeration case was already handled in
AbstractGeneratedTypeBuilder, this patch extends that support
to handle bits and union.

JIRA: MDSAL-458
Change-Id: Idc19b179274c7973ed205ffdae1d2242cbd2dbf6
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>