runners: jlink: win32: search for valid `JLink.exe`

Since "JLink.exe" is also an executable distributed with JDK's, do an
explicit search on the standard SEGGER install directories for a JTAG
"JLink.exe" before falling back to whatever is first on PATH.

Fixes #51825.

Signed-off-by: Jordan Yates <jordan@embeint.com>