fix(java): give jdtls memory back when idle and stop it showing as not responding (#1137)

jdtls ran on the parallel collector, which never shrinks the heap while idle, so each server kept its import/build peak committed for as long as it lived. It now runs on G1 with a periodic collection every minute and a 10–30% free-heap band, so memory goes back to the OS once the work is done (a SkyWalking checkout: 1.9 GB → 1.25–1.3 GB idle). A collector set in the JVM options still replaces ours with its tuning; setting either heap-free ratio drops both of ours.

The Equinox launcher gets -nosplash: without it its native library loads AppKit on macOS and every jdtls shows as Not Responding in Activity Monitor.

Part of #1008.

src/features/settings/languages/LanguagePages.tsx

@@ -297,7 +297,7 @@ export function JavaPage() {
         <Row
           label="JVM options"
           htmlFor={id}
-          hint="Passed to the JVM running jdtls (java.jdt.ls.vmargs), e.g. -Xmx4g. jdtls runs with -XX:+UseParallelGC -XX:GCTimeRatio=4 -XX:AdaptiveSizePolicyWeight=90 -Xmx2G -Xms100m by default; an option set here replaces the default for the same setting, and another collector (e.g. -XX:+UseG1GC) replaces the default collector options. A Lombok agent is added automatically: the one installed in Language Servers, else, when the project uses Lombok (its build, an inherited parent POM or Gradle build, or its sources' imports), the newest from the Maven / Gradle caches."
+          hint="Passed to the JVM running jdtls (java.jdt.ls.vmargs), e.g. -Xmx4g. jdtls runs with -XX:+UseG1GC -XX:G1PeriodicGCInterval=60000 -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=30 -Xmx2G -Xms100m by default; an option set here replaces the default for the same setting, and another collector (e.g. -XX:+UseZGC) replaces the default collector options. A Lombok agent is added automatically: the one installed in Language Servers, else, when the project uses Lombok (its build, an inherited parent POM or Gradle build, or its sources' imports), the newest from the Maven / Gradle caches."
         >
           <Input
             id={id}