Embed minibp into soong_ui.

This requires linking Blueprint into soong_ui. It lets us avoid the
complicated dance of Ninja files and shell scripts: now the information
as to how soong_build is built is passed directly to Blueprint using a
struct that contains all the information the command line arguments used
to contain.

The ability to run Blueprint from the command line is kept (for now).

Some variables in bootstrap/command.go needed public accessor functions
because soong_build reads them. This will be disentangled by moving the
flag parsing to soong_build.

The presence of the flag definitions in Blueprint means that soong_ui
now also accepts them. This is not a problem in practice because they
are ignored and because soong_ui itself is hidden behind a few layers of
shell scripts.

Test: Presubmits + the new bootstrap_test.sh .
Change-Id: I6dca478f356f56a8aee1e457d71439272351390b

ui/build/build.go

@@ -218,6 +218,11 @@ func Build(ctx Context, config Config, what int) {
 		what = what &^ BuildKati
 	}
 
+	if config.SkipNinja() {
+		ctx.Verboseln("Skipping Ninja as requested")
+		what = what &^ BuildNinja
+	}
+
 	if config.StartGoma() {
 		// Ensure start Goma compiler_proxy
 		startGoma(ctx, config)
@@ -290,7 +295,7 @@ func Build(ctx Context, config Config, what int) {
 		}
 
 		// Run ninja
-		runNinja(ctx, config)
+		runNinjaForBuild(ctx, config)
 	}
 
 	// Currently, using Bazel requires Kati and Soong to run first, so check whether to run Bazel last.