chore: replace deprecated String.prototype.substr() with substring()

[trivikr]

Which problem is this PR solving?

The String.prototype.substr() is deprecated.

Fixes # (issue)

Short description of the changes

This PR replaces String.prototype.substr() with String.prototype.substring()

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• CI

Checklist:

• Followed the style guidelines of this project

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.58%. Comparing base (3bf1284) to head (2de272a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5209      +/-   ##
==========================================
- Coverage   94.59%   94.58%   -0.02%     
==========================================
  Files         314      314              
  Lines        7993     7993              
  Branches     1611     1611              
==========================================
- Hits         7561     7560       -1     
- Misses        432      433       +1     

Files with missing lines	Coverage Δ
packages/opentelemetry-core/src/common/time.ts	98.55% <100.00%> (ø)
packages/opentelemetry-sdk-trace-base/src/Span.ts	97.61% <100.00%> (ø)

... and 1 file with indirect coverage changes

[trivikr]

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