RFR: 8284588: Remove GensrcCommonLangtools.gmk

[Magnus Ihse Bursie]

There's been unnecessary (near) duplication of functionality, and messy logic, in the langtools gensrc step, for a long time. (Basically since we got rid of the mercurial forest...)

This is a first attempt at cleaning this up. The file GensrcCommonLangtools.gmk is removed. This contained three pieces of functionality. 

* SetupVersionProperties was moved to GensrcCommonJdk.gmk (which was renamed to GensrcCommon.gmk). 
* PropertiesParser was only used in one place, and moved there. (jdk.compiler/Gensrc.gmk). It was also heavily rewritten to show more clearly what it actually is doing.
* SetupCompileProperties (from langtools) were replaced with calls to SetupCompileProperties (from GensrcCommon/"jdk"), which was modified slightly to accomodate for the differences. (Also the Java tool needed to be slightly modified to accept the same syntax as the JDK version of this tool.)

A reasonable follow-up is to research if the two SetupCompileProperties tools can be unified into one.

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Commit messages:
 - Unify SetupCompilePropertiesLangtools with SetupCompileProperties
 - Get rid of GensrcCommonLangtools.gmk
 - Clean up parseproperties

Changes: https://git.openjdk.java.net/jdk/pull/8167/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8167&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284588
  Stats: 367 lines in 21 files changed: 124 ins; 185 del; 58 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8167.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8167/head:pull/8167

PR: https://git.openjdk.java.net/jdk/pull/8167