Update launch script to canonicalize jarfolder

Previously, if the folder which contained the jar was a symlink the
launch script would use the symlinked folder's name when determining
the default identity.

This commit updates the launch script so that symlinks are resolved
and the canonical name of the folder which contains the jar is used
when determining the script's default identity. The behaviour when
APP_NAME has been set is unchanged.

Closes gh-5679
Closes gh-5733

spring-boot-tools/spring-boot-loader-tools/src/main/resources/org/springframework/boot/loader/tools/launch.script

@@ -37,7 +37,7 @@ while [[ -L "$jarfile" ]]; do
   cd "$(dirname "$jarfile")" || exit 1
   jarfile=$(pwd)/$(basename "$jarfile")
 done
-jarfolder="$(dirname "$jarfile")"
+jarfolder="$( (cd $(dirname "$jarfile") && pwd -P) )"
 cd "$WORKING_DIR" || exit 1
 
 # Source any config file