Implementation uploaded for review. Includes unit tests but does not
yet handle prebuilts, that will come in a future change once some
more general issues with prebuilts and namespaces is resolved.

See README.md#Visibility for details of what this does and how to use
it.

Bug: 112158820
Test: add visibility rules for core library modules, make core-tests
Change-Id: I8ec980554398ad6f2d42043ce518f811a35da679

The built reference documentation is now hosted publicly.

Test: check the link in gitiles
Change-Id: I69c90f2d74f1e7535054aed115930a293057ad48

On the recent versions, the module types help
is generated into $OUT_DIR/soong/docs/soong_build.html

Test: make && ls -l out/soong/docs/soong_build.html
Change-Id: Ib7522a417fd5467f19d7393672a592d349f276f4

Test: make online-sac-docs

Bug: 120866204
Change-Id: I4560a32ec2cb29aaaa9e9048d4ed075d09a44d13

Change-Id: Ia14b1a5b1f96c3a70465eb1c34367deb5c1d4234

Test: none
Change-Id: I507b7118bfc240166dced0cc26ab523ce56f68a2

Bug: 71906438
Test: none
Change-Id: Ic18f2dc5d91b30ff2b5beb8047d98591ba70ee00

Some tools (i.e. you-complete-me) make use of a 'compdb' file
(compile_commands.json) that records (among other things) the
arguments needed to compile a file. These tools can use this with
libclang to provide semantic completions and perform other IDE
actions. This CL adds support for soong to generate a (simple)
compile_commands.json file.

Test: make SOONG_GEN_COMPDB=1 SOONG_LINK_COMPDB_TO=$ANDROID_BUILD_TOP nothing
      examine $ANDROID_BUILD_TOP/compile_commands.json

Change-Id: I751bb344b90dfcdad1dfd71c2a85bacd345f0464

Test: check gitiles view
Change-Id: I2fa4fa5f7ee91ba586e1900542c8c334eb727a6b

Bug: 65683273
Test: Read README.md

Change-Id: I179c085e123858ae425515ac6bbf4b272c245a2e

Test: m clean && m -j java and java_test.go

Change-Id: I110a0ff029448d3319aed2788d25d90a6c1a7fa0

Test: None
Change-Id: Ie2ad921974dc4ff82a3c6308736830cacfebf806

filegroup is a module that contains a list of files, and can be used
to export files across package boundaries.  filegroups (and genrules)
can be referenced from srcs properties of other modules using the
syntax ":module".

Test: m -j
Change-Id: I3d6fc4819c0b4225b474e0ad42f0d947f55a5961

Use go/Android.bp link, add a little more on androidmk conversions.

Test: none
Change-Id: Ibe2be4ad54b6d9a8954d7efbb40d04dc54c8dbf2

Change-Id: I07970cddefb981f6708b276ac5b04d311d1843d9