memory: Simplify names of backend functions

[stotko]

The backend implementation of memory used the term "dispatch" to indicate that the backend is performing the operation based on the passed memory type. However, this just makes the names more complex. Furthermore, auxiliary functions for actually calling the backend implementation are defined as well which, however, are never exposed outside and just add another layer of indirection. Simplify the name and call convention to reduce bloat and prepare the backends for future feature additions.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 97.45%. Comparing base (8a0abf1) to head (7daf62b).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/stdgpu/openmp/impl/memory.cpp	50.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #442      +/-   ##
==========================================
+ Coverage   97.42%   97.45%   +0.02%     
==========================================
  Files          32       32              
  Lines        2603     2594       -9     
==========================================
- Hits         2536     2528       -8     
+ Misses         67       66       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.