[SharedCache] Simplify MMappedFileAccessor::Read* methods

This change is mostly motivated by simplifying the code, but it also
brings minor correctness and performance benefits.

1. The pointer returned by mmap is stored as a uint8_t* rather than
   void* as that is how it is used. This reduces how often it needs to
   be cast to a different type before it is used.
2. Read methods for primitives delegate to a new Read template function
   that in turn delegates to the general-purpose `Read(void* dest, size_t
   address, size_t length)`. This improves the consistency of bounds
   checking and simplifies the code. The compiler is more than willing
   to inline this so we get less repetition with no overhead.
3. ReadNullTermString now uses std::find to find the nul byte and
   directly constructs the string from that range of bytes. This removes
   an unnecessary allocation that was previously being forced by the use
   reserve followed by shrink_to_fit. It also avoids repeated
   reallocation for longer strings as they grew past the the reserved
   size as they were being built up a character at a time.

0 files changed, 0 insertions, 0 deletions