Add `Buffer.stringLength(input[, encoding])`, the counterpart of
`Buffer.byteLength()`: it returns the number of UTF-16 code units that
`buf.toString(encoding)` would produce, without decoding.
For UTF-8 the count is computed with simdutf. Invalid input is counted
with the same maximal-subpart replacement that the decoder applies, so
the result always matches `toString().length`. The other encodings are
computed from `byteLength` alone.
This lets code that accumulates streamed input check the result against
`buffer.constants.MAX_STRING_LENGTH` and size its memory budget before
decoding.
Refs: https://github.com/nodejs/node/issues/66062
Signed-off-by: Matteo Collina <hello@matteocollina.com>
PR-URL: https://github.com/nodejs/node/pull/66064
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>
