Optimized inlining of njs_values_strict_equal().

Optimized inlining of njs_values_strict_equal().

This function is often called inside loops and basically it does only a few cmp
instructions that can be inlined.

The more complex part related to comparing of two strings is functionally
identical to njs_string_eq(), but contains an optimization that avoids memcmp()
when strings have different lengths.  This optimization has been merged into
njs_string_eq().

No functional changes.