Simplied conversions from strings to numbers

[yitam]

When using client buffers, fetching strings as doubles or integers is inconsistent across platforms. Simplified the corresponding helper methods. Also, no need to keep the numbers to wide strings functions because the drivers no longer convert numeric values to wide strings.

[coveralls]

Coverage increased (+0.3%) to 75.376% when pulling ad8a1c7 on yitam:strtonum into d5e1d8c on microsoft:dev.

[codecov]

Codecov Report

Merging #1146 into dev will increase coverage by 0.89%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev    #1146      +/-   ##
==========================================
+ Coverage   77.87%   78.76%   +0.89%     
==========================================
  Files          24       24              
  Lines        7280     7262      -18     
==========================================
+ Hits         5669     5720      +51     
+ Misses       1611     1542      -69     

Impacted Files	Coverage Δ
...vc15/x86/php-7.4.7-src/ext/pdo_sqlsrv/pdo_stmt.cpp	81.75% <0.00%> (+0.47%)	⬆️
...p-7.4.7-src/ext/pdo_sqlsrv/shared/core_results.cpp	58.31% <0.00%> (+4.97%)	⬆️
...6/php-7.4.7-src/ext/sqlsrv/shared/core_results.cpp	72.54% <0.00%> (+6.99%)	⬆️

[v-mabarw]

Other than some remaining cleanup, looks good to me.