[build] Add make jenkins target.

[jonpryor]

The make jenkins ^0 target is for use by Continuous Integration
machines, to build everything ^1.

This is expected to take an eternity. Think hours.

$ time make jenkins
...
real    130m11.608s
user    97m22.220s
sys 18m20.522s

Of particular note is that the above "everything" includes
Release configuration builds of everything, which is something that
didn't actually work before. (Oops.)

Bump Java.Interop so that it supports building the Release
configuration, update Xamarin.Android.sln so that all required
projects are part of the Release configuration, and update
Xamarin.Android.Build.Tasks.csproj so that JCW_ONLY_TYPE_NAMES isn't
defined, as this was preventing compilation.

Fix strip(1) use: mono-runtimes.targets was trying to use
strip -S on macOS, but the value of %(_MonoRuntime.Strip) was
quoted, and thus attempted to execute "strip -S" ..., which failed.
Move the -S into a new %(_MonoRuntime.StripFlags) value.

Fixup mono-runtimes.targets and related files so that
$(MonoSourceFullPath) is used instead of a relative path. This helps
alleviate the "mental math" of determining the relative path to the
Mono checkout. Plus, the Mono checkout is supposed to be overridable,
e.g. commit d205cab, and using $(MonoSourceFullPath) supports that.

Download and install android.jar for all supported API levels.

Fix the Mono.Android.csproj build so that Mono.Android.dll is
stored in a per-API-level intermediate directory. Otherwise, if e.g.
API-10 is built after API-23, the API-23 version will be installed,
but the JCW build will fail. Additionally, API-24 requires using
javac -source 1.8 -target 1.8, not 1.6.

Fix Mono.Android/metadata to use the correct merge.SourceFile
filename of Profiles/api-24.xml.in. Without that fix, API-24 won't
build because NumericShaper.GetContextualShaper() is emitted twice,
and the C# compiler doesn't like that.

Disable use of -lz when building for Windows. Windows doesn't
contain a Z.DLL to link against.

[grendello]

Do we really need anything below 9 here?

[jonpryor]

Yes, for the same reason that $(ALL_FRAMEWORKS) has a bunch of - values.

That reason being that $(FRAMEWORKS) and others use the $(word n,text) function, and $(word) requires 1-based values. If $(ALL_API_LEVELS) doesn't have 1..9, then $(word 10, $(ALL_API_LEVELS) won't be 10, which means $(word 10, $(ALL_FRAMEWORKS) won't be v2.3, which greatly hampers the ability, within make, to associate those values.

This might be a sign that this associate shouldn't be done within Make; perhaps it should be done within Mono.Android.targets? I'm not certain how that would work either.

[dellis1972]

@jonpryor @grendello looks ok to me.

[grendello]

It looks good to me, except for one thing - unless I'm mistaken, the change to android-toolchain.projitems will cause a simple make to download and build all the platforms. Can we have a filter on API level to narrow this set to, by default, just the latest platform?

[jonpryor]

@grendello: That is correct.

Should that be fixed before merging this PR? Or done separately? (I'd really like to get this in so that @duncanmak can start using it...)

[grendello]

I think separately is fine