feat(RadioInterface): Tx power gain calculation rework

[ndoo]

• 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.

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
  • RAK WisBlock 4631
  • Seeed Studio T-1000E tracker card
  • Other (please specify below)
    • XIAO BLE

> meshtastic --get lora.tx_power
Connected to radio
lora.tx_power: 27
Completed getting preferences

INFO  | ??:??:?? 0 Start meshradio init
INFO  | ??:??:?? 0 Radio freq=922.875, config.lora.frequency_offset=0.000
INFO  | ??:??:?? 0 Set radio: region=MY_919, name=LongFast, config=0, ch=15, power=27
INFO  | ??:??:?? 0 myRegion->freqStart -> myRegion->freqEnd: 919.000000 -> 924.000000 (5.000000 MHz)
INFO  | ??:??:?? 0 numChannels: 20 x 250.000kHz
INFO  | ??:??:?? 0 channel_num: 16
INFO  | ??:??:?? 0 frequency: 922.875000
INFO  | ??:??:?? 0 Slot time: 28 msec
INFO  | ??:??:?? 0 Requested Tx power: 27 dBm; Device LoRa Tx gain: 7 dB
INFO  | ??:??:?? 0 Final Tx power: 20 dBm
INFO  | ??:??:?? 0 SX126x init result 0
INFO  | ??:??:?? 0 Frequency set to 922.875000
INFO  | ??:??:?? 0 Bandwidth set to 250.000000
INFO  | ??:??:?? 0 Power output set to 20

[ndoo]

Just did a test to confirm that trying to set higher than supported Tx power (either by the PA or by SX1262 etc.) doesn't break, it just sets the maximum the variant allows.

INFO  | ??:??:?? 3 Requested Tx power: 30 dBm; Device LoRa Tx gain: 7 dB
INFO  | ??:??:?? 3 Final Tx power: 23 dBm
INFO  | ??:??:?? 3 SX126x init result 0
INFO  | ??:??:?? 3 Frequency set to 922.875000
INFO  | ??:??:?? 3 Bandwidth set to 250.000000
INFO  | ??:??:?? 3 Power output set to 22