Clarify ownership model of CiffComponent::pData_

[kevinbackhouse]

This is a stepping stone to some other changes that I would like to make to DataBuf. In particular, I would like to get rid of the release method and instead use std::move for ownership transfers of DataBuf.

This changes simplifies the ownership model of CiffComponent::pData_. It is usually a pointer into read-only memory owned by somebody else, but when isAllocated_ == true, it owns the memory. This, combined with the fact that we sometimes do arithmetic on the pointer, makes me nervous. I have changed it so that pData_ always points to data owned by somebody else. I added a field named storage_ for when CiffComponent needs to own the data itself.

[codecov]

Codecov Report

Merging #1930 (3b0d827) into main (774e662) will increase coverage by 0.24%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main    #1930      +/-   ##
==========================================
+ Coverage   60.87%   61.12%   +0.24%     
==========================================
  Files          96       96              
  Lines       19041    19055      +14     
  Branches     9726     9743      +17     
==========================================
+ Hits        11591    11647      +56     
+ Misses       5138     5092      -46     
- Partials     2312     2316       +4     

Impacted Files	Coverage Δ
src/crwimage_int.hpp	84.61% <71.42%> (+0.24%)	⬆️
src/crwimage_int.cpp	74.07% <100.00%> (+0.03%)	⬆️
src/makernote_int.cpp	67.62% <0.00%> (-0.72%)	⬇️
src/exiv2.cpp	57.85% <0.00%> (ø)
src/futils.cpp	72.06% <0.00%> (ø)
src/properties.cpp	73.36% <0.00%> (ø)
src/pentaxmn_int.cpp	72.92% <0.00%> (+0.23%)	⬆️
src/convert.cpp	53.84% <0.00%> (+0.34%)	⬆️
src/value.cpp	73.18% <0.00%> (+0.46%)	⬆️
src/tags_int.cpp	77.05% <0.00%> (+0.71%)	⬆️
... and 2 more

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[kevinbackhouse]

Thanks @neheb!