Support for f-strings

[s-hadinger]

Major enhancement discussed in Tasmota Berry support. The Berry parser now supports the equivalent for Python's f-strings.

This feature is pure syntactic sugar and purely re-writes the f-string as follows:

• internally a command format("<template", <arguments>) is generated from the f-string. This is done by the lexer that re-writes the f-string (like a transpiler) and sends the re-written part to the parser. Hence there is no code difference nor any impact to the runtime.
• { and } need to be escaped as {{ and }}
• inserts are formed as {<expr>:<format>} and are transformed as %<format> followed by <expr> as argument
• if <format> is omitted, the string qualifier %s is used
• if <format> starts with %, this character is ignored
• a special case {<expr>=:<format>} is useful for debugging are writes the literal <expr> in the format.

Examples: f-strings followed by their equivalent

# let's initialize some variables
var a = 1
var f = 3.1415
var s = 'foobar{0}'

f"foobar{{1}}"
format("foobar{1}")
# 'foobar{1}'

# integers are automatically converted to strings
f'1 + 1 is {1+1}'
format('1 + 1 is %s', 1+1)
# '1 + 1 is 2'

f"p = {f:.2f}"
format("p = %.2f", f)
# 'p = 3.14'

f"s = {s} a = {a} f = {f:.1f}"
format("s = %s a = %s f = %.1f", s, a, f)
# 's = foobar{0} a = 1 f = 3.1'

f"{s=} {a+1=} {f=:.1f}"
format("s=%s a+1=%s f=%1.f", s, a+1, f)
# 's=foobar{0} a+1=2 f=3.1'