Make sdkDep/decodeSdkDep the source of truth about the sdk

Previously, different parts of the build used different sources of
information about the SDK (i.e. the default libraries) against which
a Java module aimed at the device was built. Some used the sdk_version
property, others used the no_standard_libs or no_framework_libs, some
used a combination of all three.

That lead to inconsistent handling in the code, e.g. some parts treated
no_standard_libs: true as implying no_framework_libs: true and others
did not, and also in the build files, e.g. some modules specified
no_framework_libs: true and sdk_version: "system_current" which makes
no sense, or no_standard_libs: true and sdk_version: "core_current"
which are inconsistent.

This is the first step in a refactoring to simplify the sdk selection
process by replacing the no_standard_libs/no_framework_libs properties
with some extra options for the sdk_version property. This change
consists of:
1) Extra functions sdkContext to access the no_standard_libs and
   no_framework_libs properties.
2) Extra field/functions in sdkDep to store and access the value of
   no_standard_libs/no_framework_libs.
3) Changes to decodeSdkDep(...) to pass the values of the no_...
   properties through to the returned sdkDep.
4) Change all code that accesses the no_... properties directly to
   call decodeSdkDep(...) to get an sdkDep object and then accessing
   the values of the no_... properties from there.

The accessor functions on sdkDep are called has...() rather than
no...() as most callers of the methods invert the value anyway and
!no...() is harder to reason about than has...().

The hasFrameworkLibs() function returns true if and only if
no_standard_libs and no_framework_libs are false. That is consistent
with all but one usage of the no_framework_libs property and that is
not affected by it.

Bug: 134566750
Test: m droid
Change-Id: I196e3304e8bd802fb154e897397b0dd337f868e2
Exempt-From-Owner-Approval: Colin has already given +2 modulo some
    minor nits and this blocking other changes.