Improve property comments for docs

Improve the comments associated with properties to work better with
Blueprint's auto-documenting feature.

Make all properties structs into named types so that thet types can be
found using reflection and cross-referenced to the source code to
auto-extract docs.

Remove the leading <property>: text from properties, the documentation
will include the lowercased name of the property.

Add filter tags to the nested arch properties.

Change-Id: I4ef5db86358886fe61456c24eb2dbe6f7b876115
diff --git a/genrule/genrule.go b/genrule/genrule.go
index ea30e3d..b393831 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -40,21 +40,23 @@
 	HostToolPath() string
 }
 
+type generatorProperties struct {
+	// command to run on one or more input files.  Available variables for substitution:
+	// $in: one or more input files
+	// $out: a single output file
+	// $srcDir: the root directory of the source tree
+	// The host bin directory will be in the path
+	Cmd string
+
+	// name of the module (if any) that produces the host executable.   Leave empty for
+	// prebuilts or scripts that do not need a module to build them.
+	Tool string
+}
+
 type generator struct {
 	common.AndroidModuleBase
 
-	properties struct {
-		// cmd: command to run on one or more input files.  Available variables for substitution:
-		// $in: one or more input files
-		// $out: a single output file
-		// $srcDir: the root directory of the source tree
-		// The host bin directory will be in the path
-		Cmd string
-
-		// tool: name of the module (if any) that produces the host executable.   Leave empty for
-		// prebuilts or scripts that do not need a module to build them.
-		Tool string
-	}
+	properties generatorProperties
 
 	tasks taskFunc
 
@@ -146,10 +148,10 @@
 }
 
 type genSrcsProperties struct {
-	// srcs: list of input files
+	// list of input files
 	Srcs []string
 
-	// output_extension: extension that will be substituted for each output file
+	// extension that will be substituted for each output file
 	Output_extension string
 }
 
@@ -169,9 +171,9 @@
 }
 
 type genRuleProperties struct {
-	// srcs: list of input files
+	// list of input files
 	Srcs []string
 
-	// out: name of the output file that will be generated
+	// name of the output file that will be generated
 	Out string
 }