Add get_ap() method to WiFi

[anatoly-savchenkov]

What does this implement/fix?

Adds get_ap() method to make WiFi AP details available to applications. Can be useful to get auto-generated AP SSID name in case of fallback AP or captive portal.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP32 IDF
• ESP8266

Example entry for config.yaml:

# Example config.yaml
esphome:
  name: ${devicename}
  name_add_mac_suffix: true

wifi:
  ap: {} # This spawns an AP with the device name and mac address with no password.

captive_portal:

# Nextion lambda to generate QR code with WiFi settings for captive portal
      lambda: |-
        id(disp).set_component_text_printf("qr_wifi", "WIFI:T:nopass;S:%s;P:;;", wifi::global_wifi_component->get_ap().get_ssid().c_str());

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[GregJArnold]

Should do the trick.