Don't override GDK_SCALE if already set

### Description

Currently Netbeans does GDK_SCALE=2 if a DPI above 192 is detected. On my system, this leads to really large fonts and windows. I have set GDK_SCALE=1 which makes the size of NetBeans equal to all other gui components in size (Using Gnome 44 desktop on Arch).

What I have in mind in the /usr/bin/netbeans shell script:

```shell
# First check if GDB_SCALE was set. If the xrdb command does not exist, no action will be taken.
if [ -n "$GDK_SCALE" ];
then
echo "GDK_SCALE was set, not overriding: GDK_SCALE=$GDK_SCALE"
elif [ "`command xrdb -query 2> /dev/null | grep Xft.dpi | cut -d ':' -f2 | xargs`" = 192 ]
then
echo "Detected 2x HiDPI scaling in Xft.dpi setting; setting GDK_SCALE=2"
export GDK_SCALE=2
fi
```

### Use case/motivation

This change allows you to pre-configure a local preference, without forcefully overriding GDK_SCALE.

### Related issues

https://github.com/apache/netbeans/pull/3113

### Are you willing to submit a pull request?

Yes

Start with the /usr/bin/netbeans shell script and inspect the existing GDK_SCALE assignment and xrdb-based DPI detection. Verify that an existing GDK_SCALE value is preserved, automatic scaling still occurs when it is unset, and the script remains valid with or without xrdb.

Written by the indexing model from the issue text.