Allow user to enable Web Serial

[robd003]

Description

I'd like to use Web Serial to flash my ESP32 devices from the browser. Unfortunately Brave doesn't even give me the option to enable Web Serial.

Steps to reproduce

1. Navigate to https://esphome.github.io/esp-web-tools/

Actual result

Brave disabled Web Serial and so the user is limited and has to install Chrome (yuck!)

Expected result

Give the user the choice to enable web serial for a domain

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Version 1.67.116 Chromium: 126.0.6478.71 (Official Build) (arm64)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

No response

[robd003]

Ideally the way this would work is navigator.serial would be undefined, but when attempted to be accessed the user would be prompted to enable the web serial API. This way there would be no fingerprinting concerns, but the feature could still be enabled when a user needed it.

Brave could treat it just like a request for mic or camera access

[rebron]

Closing as duplicate of #38791 and fixed in 1.69.x