chore(stdlib): Optimize String.trim

[spotandjake]

This optimizes String.trim by avoiding the double allocation of a new string after each separate string. Now we only allocate a new string once weve trimmed both sides.

I think this optimization can also close: #982 even though we still do two seperate iterations combing them would likely lead to unmaintainable code with a minimal performance increase.

[phated]

I don't have the energy to debate about a single loop 😛