RFR 8209064: Make intellij support more robust after changes for 2018.2

[Maurizio Cimadamore]

Hi,
last week I submitted an 'emergency' patch to fix intellij project 
support after 2018.2 changes. The goal of these changes was to move the 
build.xml ant file out of the .idea folder, as the IDE no longer 
supported DOM indexing in such folders (as a result of 
https://youtrack.jetbrains.com/issue/IDEA-189915). As a workaround, I 
tweaked the scripts to copy build.xml in the build folder.

Thinking more about this issue, there's a more robust fix possible, 
which doesn't involve moving files to the build folder (which could be 
potentially unreliable, depending on how people build the JDK). In fact, 
the best solution is to leave build.xml where it is, and fix the 
remaining configuration files to point at it. This allows to revert all 
changes in the scripts that set up the project configuration 
(bin/idea.sh for JDK, and make/langtools/build.xml for langtools).

For the langtools project a bit more changes were necessary, given that 
in langtools we did not have a 'template' folder - and all intellij 
files were dumped onto the same path. So I had to move the configuration 
langtools files (all but build.xml) under a new template folder (located 
under make/langtools/intellij/make) and place build.xml outside it. Then 
tweak the build.xml script to work off this new template folder. These 
are all small conceptual changes, but the impact on the webrev is quite 
biggie (because of file renaming etc.).

I also took the chance to fix some issues with the JDK project ANT 
configuration (see changes in make/idea/template/workspace.xml), as the 
last changes did not update the location of the ant file used here - as 
a result no ant target entries were showing up under the Build menu.

Webrev here:

http://cr.openjdk.java.net/~mcimadamore/8209064/

Cheers
Maurizio