improved ScriptRuntime.toPrimitive() (taken from #1611 done by @tonygermano)

[rbri]

this is an excerpt from PR #1611 done by @tonygermano (commit 9664e77, e17cc25)

• more standard compliant implementation of ScriptRuntime.toPrimitive();
  • have not used the Optional for more backward compatibility
  • have changed the code a bit to be more in sync with the spec (explicit if stmt's)
• improved support for Symbol/BigInt in equals and compare

I did this to make it possible to merge this improvement soon - at least this is my hope. Will extract more smaller commits if this is merged.

[gbrail]

I'd like to keep the super-pedantic warnings from errorprone clean. (I haven't made them errors yet but I'm thinking about it.) Can you please check these?

/Users/gbrail/src/rhino/rhino/src/main/java/org/mozilla/javascript/ScriptRuntime.java:3995: warning: [UnnecessaryParentheses] These grouping parentheses are unnecessary; it is unlikely the code will be misinterpreted without them
if ((isSymbol(val1)) || (isSymbol(val2))) {
^
(see https://errorprone.info/bugpattern/UnnecessaryParentheses)
Did you mean 'if ( isSymbol(val1) || (isSymbol(val2))) {'?
/Users/gbrail/src/rhino/rhino/src/main/java/org/mozilla/javascript/ScriptRuntime.java:3995: warning: [UnnecessaryParentheses] These grouping parentheses are unnecessary; it is unlikely the code will be misinterpreted without them
if ((isSymbol(val1)) || (isSymbol(val2))) {
^
(see https://errorprone.info/bugpattern/UnnecessaryParentheses)
Did you mean 'if ((isSymbol(val1)) || isSymbol(val2)) {'?

[rbri]

errorprone done and rebased

[gbrail]

Great, thanks!