feat(RadioInterface): Tx power gain calculation rework (#6796)

- Rename REGULATORY_GAIN_LORA to TX_GAIN_LORA
- Move gain-based Tx power clamping from RadioInterface::applyModemConfig() to RadioInterface::limitPower()
  - User-configured Tx power now matches the Tx power out of the device connector
- Re-order [LoRa Chip]Interface.cpp limitPower() to take place before the final Tx power clamping so we clamp based on the pre-PA Tx power rather than user-configured Tx power

Tested on XIAO BLE variant.

Signed-off-by: Andrew Yong <me@ndoo.sg>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mesh/RF95Interface.cpp

@@ -122,11 +122,11 @@ bool RF95Interface::init()
     power = dacDbValues.db;
 #endif
 
+    limitPower();
+
     if (power > RF95_MAX_POWER) // This chip has lower power limits than some
         power = RF95_MAX_POWER;
 
-    limitPower();
-
     iface = lora = new RadioLibRF95(&module);
 
 #ifdef RF95_TCXO