Introduce product variables to select Java code coverage paths in Soong.

Introduce product variables `JavaCoveragePaths` and
`JavaCoverageExcludePaths` (resp. populated from environment variables
`JAVA_COVERAGE_PATHS` and `JAVA_COVERAGE_EXCLUDE_PATHS`). Use them to
control which Java modules are candidate for instrumentation based on
their source path. By default (when `JavaCoveragePaths` is empty),
have all Java module be candidate for instrumentation, to preserve the
existing behavior.

Test: export EMMA_INSTRUMENT=true \
        && export EMMA_INSTRUMENT_FRAMEWORK=true \
        && export JAVA_COVERAGE_PATHS=art \
        && m
Bug: 158212027
Bug: 156284897
Change-Id: Ibe9c1f41ed6110867411952689c5a7ad6536f277

java/java.go

@@ -601,7 +601,9 @@ type jniLib struct {
 }
 
 func (j *Module) shouldInstrument(ctx android.BaseModuleContext) bool {
-	return j.properties.Instrument && ctx.Config().IsEnvTrue("EMMA_INSTRUMENT")
+	return j.properties.Instrument &&
+		ctx.Config().IsEnvTrue("EMMA_INSTRUMENT") &&
+		ctx.DeviceConfig().JavaCoverageEnabledForPath(ctx.ModuleDir())
 }
 
 func (j *Module) shouldInstrumentStatic(ctx android.BaseModuleContext) bool {