)

The result of utf-8 encoding a string was represented in a string, where
each individual character represented a single byte according to its
character code. All usages of this data were interested in the byte
itself, so this required conversion from a character back to its code.
This commit simply stores the individual bytes in array to avoid the
conversion. This yields a ~10% performance improvement for i18n message
ID computation.

PR Close #39694

Message ID computation makes extensive use of big integer
multiplications in order to translate the message's fingerprint into
a numerical representation. In large compilations with heavy use of i18n
this was showing up high in profiler sessions.

There are two factors contributing to the bottleneck:

1. a suboptimal big integer representation using strings, which requires
repeated allocation and conversion from a character to numeric digits
and back.
2. repeated computation of the necessary base-256 exponents and their
multiplication factors.

The first bottleneck is addressed using a representation that uses an
array of individual digits. This avoids repeated conversion and
allocation overhead is also greatly reduced, as adding two big integers
can now be done in-place with virtually no memory allocations.

The second point is addressed by a memoized exponentiation pool to
optimize the multiplication of a base-256 exponent.

As an additional optimization are the two 32-bit words now converted to
decimal per word, instead of going through an intermediate byte buffer
and doing the decimal conversion per byte.

The results of these optimizations depend a lot on the number of i18n
messages for which a message should be computed. Benchmarks have shown
that computing message IDs is now ~6x faster for 1,000 messages, ~14x
faster for 10,000 messages, and ~24x faster for 100,000 messages.

PR Close #39694

)

The result of utf-8 encoding a string was represented in a string, where
each individual character represented a single byte according to its
character code. All usages of this data were interested in the byte
itself, so this required conversion from a character back to its code.
This commit simply stores the individual bytes in array to avoid the
conversion. This yields a ~10% performance improvement for i18n message
ID computation.

PR Close #39694