clang-format: [JS] do not wrap before any `is`.

[mprobst]

Summary

is type annotations can occur at any nesting level. For example:

function x() {
  return function y(): a is B { ... };
}

Breaking before the is above breaks TypeScript parsing the code. This
change prevents the wrap.

lib/Format/TokenAnnotator.cpp

if (Right.NestingLevel == 0 &&
         (Left.Tok.getIdentifierInfo() ||
          Left.isOneOf(tok::r_square, tok::r_paren)) &&
         Right.isOneOf(tok::l_square, tok::l_paren))
       return false; // Otherwise automatic semicolon insertion would trigger.
     if (Left.is(TT_JsFatArrow) && Right.is(tok::l_brace))
       return false;
     if (Left.is(TT_JsTypeColon))
       return true;
-    if (Right.NestingLevel == 0 && Right.is(Keywords.kw_is))
+    if (Right.is(Keywords.kw_is))
       return false;
     if (Left.is(Keywords.kw_in))
       return Style.BreakBeforeBinaryOperators == FormatStyle::BOS_None;
     if (Right.is(Keywords.kw_in))
       return Style.BreakBeforeBinaryOperators != FormatStyle::BOS_None;
     if (Right.is(Keywords.kw_as))
       return false; // must not break before as in 'x as type' casts
     if (Left.is(Keywords.kw_as))

unittests/Format/FormatTestJS.cpp

verifyFormat("const x = (5 + 9)\n"
                "const y = 3\n");
   // Ideally the foo() bit should be indented relative to the async function().
   verifyFormat("async function\n"
                "foo() {}",
                getGoogleJSStyleWithColumns(10));
   verifyFormat("await theReckoning;", getGoogleJSStyleWithColumns(10));
   verifyFormat("some['a']['b']", getGoogleJSStyleWithColumns(10));
   verifyFormat("x = (a['a']\n"
-               "      ['b']);", getGoogleJSStyleWithColumns(10));
+               "      ['b']);",
+               getGoogleJSStyleWithColumns(10));
+  verifyFormat("function f() {\n"
+               "  return foo.bar(\n"
+               "      (param): param is {\n"
+               "        a: SomeType\n"
+               "      }&ABC => 1)\n"
+               "}",
+               getGoogleJSStyleWithColumns(25));
 }
 
 TEST_F(FormatTestJS, AutomaticSemicolonInsertionHeuristic) {
   verifyFormat("a\n"
                "b;",
                " a \n"
                " b ;");
   verifyFormat("a()\n"