JDK 14 RFR of JDK-8224630: ElementScannerN, N > 9 should scan type parameters

[Joe Darcy]

Hello,

First on the build front, the -source/-target used in the bootstrap 
build of langtools was stuck at 9; in the change I'm proposing to update 
it to 13, the minimum boot JDK:

--- old/make/autoconf/boot-jdk.m4    2019-12-04 19:16:42.209000999 -0800
+++ new/make/autoconf/boot-jdk.m4    2019-12-04 19:16:41.925000999 -0800
@@ -345,7 +345,7 @@

    # When compiling code to be executed by the Boot JDK, force 
compatibility with the
    # oldest supported bootjdk.
-  BOOT_JDK_SOURCETARGET="-source 9 -target 9"
+  BOOT_JDK_SOURCETARGET="-source 13 -target 13"
    AC_SUBST(BOOT_JDK_SOURCETARGET)

    AC_SUBST(JAVAC_FLAGS)

This should get added to the list of files updated when the boot JDK is 
revved.

On the javax.lang.model front, with the changes for records pushed into 
JDK 14 there is now a ElementScanner14 class and I think it is time to 
address

     JDK-8224630: ElementScannerN, N > 9 should scan type parameters
     http://cr.openjdk.java.net/~darcy/8224630.0/
     CSR: https://bugs.openjdk.java.net/browse/JDK-8235371

As the bug title implies, the existing scanner classes don't touch type 
parameters, which is arguably a bug. The scanners mostly touch enclosed 
elements, but they do also touch method/constructor parameters which are 
not considered to be enclosed elements.

In its current form, the webrev relies on the test previously added for 
RoundEnvironment. However, I acknowledge it would be possible to add 
tests for this particular change.

Thanks,

-Joe