Extend IsMatchFormatter, add docs to rc.2

[axunonb]

Advanced features for IsMatchFormatter (#245)

The IsMatchFormatter is a formatter with evaluation of regular expressions.

New: The formatter can output matching group values of a RegEx.

Example:

We'll evalute this argument with IsMatchFormatter:

KeyValuePair<string, object> arg = new("theValue", "Some123Content");

a) Simple "match or no match" distinction:

This behavior is unchanged.

_ = Smart.Format("{theValue:ismatch(^.+123.+$):Okay - {}|No match content}", arg);
// Result: "Okay - Some123Content"

_ = Smart.Format("{theValue:ismatch(^.+999.+$):Okay - {}|No match content}", arg);
// Result: "No match content"

b) Show the matches in the output:

// List the matching RegEx group values
_ = Smart.Format("{theValue:ismatch(^.+\\(1\\)\\(2\\)\\(3\\).+$):Matches for '{}'\\: {m:list:| - }|No match}", arg);
// Result: "Matches for 'Some123Content': Some123Content - 1 - 2 - 3"

// Show specific matching RegEx group values with their index in the list
_ = Smart.Format("{theValue:ismatch(^.+\\(1\\)\\(2\\)\\(3\\).+$):First 2 matches in '{}'\\: {m[1]} and {m[2]}|No match}", arg);
// Result: "First 2 matches in 'Some123Content': 1 and 2"

The placeholder m is for the collection of matching RegEx group values generated by IsMatchFormatter. The collection has at least one entry for a successful match. See more details in the Microsoft docs for the GroupCollection class.

The name of the placeholder can be set with IsMatchFormatter.PlaceholderNameForMatches. "m" is the default.