init: clean up the SectionParser interface and Parser class

Remove the dependency on Action and Service from what should be a
generic Parser class.

Make ActionParser, ImportParser, and ServiceParser take a pointer to
their associated classes instead of accessing them through a
singleton.

Misc fixes to SectionParser Interface:
1) Make SectionParser::ParseLineSection() non-const as it always should
have been.
2) Use Rvalue references where appropriate
3) Remove extra std::string& filename in SectionParser::EndFile()
4) Only have SectionParser::ParseSection() as pure virtual

Document SectionParser.

Make ImportParser report the filename and line number of failed imports.

Make ServiceParser report the filename and line number of duplicated services.

Test: Boot bullhead

Change-Id: I86568a5b375fb4f27f4cb235ed1e37635f01d630
diff --git a/init/builtins.cpp b/init/builtins.cpp
index 43eb420..87d4e81 100644
--- a/init/builtins.cpp
+++ b/init/builtins.cpp
@@ -390,7 +390,7 @@
 
     // Turning this on and letting the INFO logging be discarded adds 0.2s to
     // Nexus 9 boot time, so it's disabled by default.
-    if (false) parser.DumpState();
+    if (false) DumpState();
 }
 
 /* mount_fstab