For each of these, we need to decide whether they need to be using
`expr_requires_semi_to_be_stmt`, or `expr_requires_comma_to_be_match_arm`,
which are supposed to be 2 different behaviors. Previously they were
conflated into one, causing either too much or too little
parenthesization.

This commit by itself is supposed to have no effect on behavior. All of
the call sites are updated to preserve their previous behavior.

The behavior changes are in the commits that follow.

I didn't figure out how to reach this condition with `expr` containing
`ExprKind::MacCall`. All the approaches I tried ended up with the macro
call ending up in the `StmtKind::MacCall` case below instead.

In any case, from visual inspection this is a bugfix. If we do end up
with a `StmtKind::Expr` containing `ExprKind::MacCall` with brace
delimiter, it would not need ";" printed after it.

…lse'

The change to the test is a little goofy because the compiler was
guessing "correctly" before that `falsy! {}` is the condition as opposed
to the else body. But I believe this change is fundamentally correct.
Braced macro invocations in statement position are most often item-like
(`thread_local! {...}`) as opposed to parenthesized macro invocations
which are condition-like (`cfg!(...)`).

It is impossible for expr here to be a braced macro call. Expr comes
from `parse_stmt_without_recovery`, in which macro calls are parsed by
`parse_stmt_mac`. See this part:

    let kind = if (style == MacStmtStyle::Braces
        && self.token != token::Dot
        && self.token != token::Question)
        || self.token == token::Semi
        || self.token == token::Eof
    {
        StmtKind::MacCall(P(MacCallStmt { mac, style, attrs, tokens: None }))
    } else {
        // Since none of the above applied, this is an expression statement macro.
        let e = self.mk_expr(lo.to(hi), ExprKind::MacCall(mac));
        let e = self.maybe_recover_from_bad_qpath(e)?;
        let e = self.parse_expr_dot_or_call_with(e, lo, attrs)?;
        let e = self.parse_expr_assoc_with(
            0,
            LhsExpr::AlreadyParsed { expr: e, starts_statement: false },
        )?;
        StmtKind::Expr(e)
    };

A braced macro call at the head of a statement is always either extended
into ExprKind::Field / MethodCall / Await / Try / Binary, or else
returned as StmtKind::MacCall. We can never get a StmtKind::Expr
containing ExprKind::MacCall containing brace delimiter.