This PR removes ad-hoc checks for string-like types by adding new contextual types for literal types at select locations. It addresses some of the major issues brought up in #6167 by adding strictness where users are most interested.

A literal type is inferred for any string literal in a literal match location, defined as such:

• The expression of a switch statement is a literal match location.
• The expression of a case clause is a literal match location.
• Either operand of a ===, !==, ==, or != expression is a literal match location.
• The expression within a parenthesized expression is a literal match location if the parenthesized expression itself is a literal match location.
• The expression within a type assertion (of either form) is a literal match location if the assertion expression itself is a match location.
• Either branch of a conditional expression is a literal match location if the conditional expression itself is a literal match location.
• Either operand of a || expression is a literal match location if the || expression itself is a literal match location.
• The right-side operand of a && or , expression is a literal match location if the && or , expression itself is a literal match location.

String literals can still get string literal types through contextual typing, but a check for whether a string is in a literal match location will be apply first.

This means that the following will now error:

if ("foo" === "bar") {
    // ...
}

because types "foo" and "bar" are not assignable to one another.