Berry add unicode encoding to string parsing

[s-hadinger]

Description:

Berry accept unicode encoding in string literal:

s1 = "\uF054"       # new UTF-8 encoding of unicode
s2 = "\xEF\x81\x94" # manual UTF-8 encoding
assert(s1 == s2)

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.2.7.8
• The code change is tested and works with Tasmota core ESP32 V.3.1.0.241206
• I accept the CLA.

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