java.security.Provider: port to jdk8u60 (second part)

- Add overridings for HashMap operations

Provider is a subclass of HashMap. When operations are on
Strings, they must be processed as part of the
algorithm->implementation mapping of the provider, and
so these methods must be overriden accordingly.

Newly overridden Methods added are:

compute, computeIfAbsent, computeIfPresent, getOrDefault,
merge, putIfAbsent, replace, replaceAll.

- Check that classes and constructors are public when
creating instances of services.

- Cosmetic changes like use of {@code} instead of <code>

Bug: 29631070
Test: make droid docs; vogar ProviderTest
Change-Id: I0238f4a48f31ddc50a3f18c27515023940d9ba02