Fixed compilation errors after recent changes in core

[martin-gaievski]

Description

Fixed compilation errors after changes in core Strings classes (opensearch-project/OpenSearch#9103)

Check List

• All tests pass
• Commits are signed as per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #1031 (675c393) into main (0d97aba) will decrease coverage by 0.24%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1031      +/-   ##
============================================
- Coverage     85.33%   85.10%   -0.24%     
+ Complexity     1149     1144       -5     
============================================
  Files           154      154              
  Lines          4692     4692              
  Branches        425      425              
============================================
- Hits           4004     3993      -11     
- Misses          497      506       +9     
- Partials        191      193       +2     

Files Changed	Coverage Δ
...opensearch/knn/index/mapper/MethodFieldMapper.java	85.71% <100.00%> (ø)

... and 2 files with indirect coverage changes

[martin-gaievski]

BWC tests will fail now, there is an issue with core 2.10.0 build

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-1031-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 0a7fc4e3d382c17bcd3537a6d625eec07f23085d
# Push it to GitHub
git push --set-upstream origin backport/backport-1031-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-1031-to-2.x.