Fix pyocd launch

[jreineckearm]

Fixes

N/A

Changes

• Removed pyOCD auto-fill of --target and --pack. This will be obsolete with the first pyOCD dev drops that use --cbuild-run.
• Resolve with substituted variables for pyOCD now that the commands for the two above pyOCD CLI args are no longer needed. Moves resolving to the latest possible point in time.
• Use future pyOCD --cbuild-run CLI arg if debug launch config item provided. NOTE: Remove cbuildRunFile setting if using an older pyOCD version. Otherwise launching it will fail.
• Prepend auto-filled gdbserver arg for pyOCD. Must be first argument. Relevant if mixing user provided server args with auto-filled ones.
• Removed reset before load in pyOCD init commands.
• More refactoring.
• README update to explain current setup steps for pyOCD debug (for when pyOCD is included in extension).

Screenshots

Checklist

[omarArm]

I think that the best course is to halt the device using monitor halt and then load. Obviously if there was no pre-existing image on the device already, then no need to halt