clang-format: [JS] fix `of` detection.

[mprobst]

Summary

of is only a keyword when after an identifier, but not when after
an actual keyword.

Before:

return of (a, b, c);

After:

return of(a, b, c);

[djasper]

Looks good.

lib/Format/TokenAnnotator.cpp

if (Right.is(tok::l_paren)) {
         return true;
     }
     if ((Left.isOneOf(Keywords.kw_let, Keywords.kw_var, Keywords.kw_in,
                       tok::kw_const) ||
          // "of" is only a keyword if it appears after another identifier
          // (e.g. as "const x of y" in a for loop), or after a destructuring
          // operation (const [x, y] of z, const {a, b} of c).
          (Left.is(Keywords.kw_of) && Left.Previous &&
-          (Left.Previous->Tok.getIdentifierInfo() ||
+          (Left.Previous->Tok.is(tok::identifier) ||
            Left.Previous->isOneOf(tok::r_square, tok::r_brace)))) &&
         (!Left.Previous || !Left.Previous->is(tok::period)))
       return true;
     if (Left.isOneOf(tok::kw_for, Keywords.kw_as) && Left.Previous &&
         Left.Previous->is(tok::period) && Right.is(tok::l_paren))
       return false;
     if (Left.is(Keywords.kw_as) &&
         Right.isOneOf(tok::l_square, tok::l_brace, tok::l_paren))

unittests/Format/FormatTestJS.cpp

TEST_F(FormatTestJS, ReservedWords) {
   // JavaScript reserved words (aka keywords) are only illegal when used as
   // Identifiers, but are legal as IdentifierNames.
   verifyFormat("x.class.struct = 1;");
   verifyFormat("x.case = 1;");
   verifyFormat("x.interface = 1;");
   verifyFormat("x.for = 1;");
   verifyFormat("x.of();");
   verifyFormat("of(null);");
+  verifyFormat("return of(null);");
   verifyFormat("import {of} from 'x';");
   verifyFormat("x.in();");
   verifyFormat("x.let();");
   verifyFormat("x.var();");
   verifyFormat("x.for();");
   verifyFormat("x.as();");
   verifyFormat("x.instanceof();");
   verifyFormat("x.switch();");