RFR JDK-8073893: Enable charsets build system to configure euc_tw into java.base module/sun.nio.cs

[Xueming Shen]

Hi, please help review the changes for

issue: 8073893: Enable charsets build system to configure euc_tw into java.base module/sun.nio.cs
webrev: http://cr.openjdk.java.net/~sherman/8073893/webrev

This is the continuation of JDK-8073152, in which we updated the build mechanism to be move
some sun.nio.cs.ext charsets from the jdk.charsets module into the java.base module. The
proposed change in this RFE is to do the same thing to enable the EUC_TW (huge, about
200k) to be built into the java.base/sun.nio.cs as well, for Solaris platform.

The change also includes a small update to move the x-COMPOUND_TEXT into the configure
file for the extended charsets provider, in stead of being hard-coded in the source file.

Thanks!
-Sherman