New: Add prefer-regex-literals rule (fixes #12238)

[mdjermanovic]

What is the purpose of this pull request? (put an "X" next to item)

[X] New rule #12238

Examples of incorrect code for this rule:

new RegExp("abc");
new RegExp("abc", "u");
RegExp("abc");
RegExp("abc", "u");
new RegExp("\\d\\d\\.\\d\\d\\.\\d\\d\\d\\d");
RegExp(`^\\d\\.$`);
new RegExp(String.raw`^\d\.$`);

Examples of correct code for this rule:

/abc/;
/abc/u;
/\d\d\.\d\d\.\d\d\d\d/;
/^\d\.$/;
// RegExp constructor is allowed for dynamically generated regular expressions
new RegExp(pattern);
RegExp("abc", flags);
new RegExp(prefix + "abc");
RegExp(`${prefix}abc`);
new RegExp(String.raw`^\d\. ${sufix}`);

What changes did you make? (Give an overview)

Added new rule prefer-regex-literals

Is there anything you'd like reviewers to focus on?

[platinumazure]

Some minor documentation tweaks and one question.

Also, I wanted to note that you can pass parserOptions to the RuleTester constructor, and have them be the default on all tests. I don't personally think there is much value in having the parserOptions set for each test since, if the user tried to use template literals without the right ecmaVersion, the rule wouldn't even run. So, if you want to save some lines, you could pass parserOptions: { ecmaVersion: 2015 } to the RuleTester constructor. But I don't feel strongly about this at all.

[mysticatea]

LGTM, thank you!

Requests were addressed