Change type of Resize capacity from int to size_t

[ThomsonTan]

Parameter new_capacity for RuntimeContext::Resize() should be in type size_t instead of int, to be consistent with size_.

This could cause issue because size_t could have larger range than int (this is the case on Windows 64-bit system which is in LLP64 data model), so convert size_t to int could cause data loss.

[codecov]

Codecov Report

Merging #346 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #346   +/-   ##
=======================================
  Coverage   94.71%   94.71%           
=======================================
  Files         154      154           
  Lines        6847     6847           
=======================================
  Hits         6485     6485           
  Misses        362      362           

Impacted Files	Coverage Δ
...pi/include/opentelemetry/context/runtime_context.h	97.36% <100.00%> (ø)