LVGL add lv.str_arr

[s-hadinger]

Description:

Add missing lv.str_arr class used by lv_btnmatrix_set_map and lv_msgbox_create.

Example:

var  btns = lv.str_arr(["Apply", "Close", ""])
var mbox1 = lv.msgbox(haspmota.scr, "Test", "Test1", btns, true)

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.5
• The code change is tested and works with Tasmota core ESP32 V.2.0.14
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass