buffer: always let indexOf look at odd indexes
Previously, buffer.indexOf would look only at even indexes when the encoding is UTF-16. This behavior is undocumented and unintuitive.
Detemplatize string_search.h because it is now used with only one type.
Fixes: https://github.com/nodejs/node/issues/26448
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines