Replace boxing Hashtable in Grid's Measure, improve performance

[h3xds1nz]

Description

Replaces boxing Hashtable in Grid's MeasureOverride, improving performance when doing cells calculations.

The key has been changed to a readonly struct to further improve performance.

7 cells benchmark (register+enumerate)

Method	children	Mean [ns]	Error [ns]	StdDev [ns]	Code Size [B]	Gen0	Allocated [B]
Original	Child(...)on[7] [21]	283.2 ns	5.66 ns	10.21 ns	4,421 B	0.0873	1464 B
PR__EDIT	Child(...)on[7] [21]	112.2 ns	2.23 ns	2.65 ns	4,495 B	0.0324	544 B

Customer Impact

Improved performance, decreased allocations.

Regression

No.

Testing

Local build, benchmark.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 34 lines in your changes missing coverage. Please review.

Project coverage is 11.36855%. Comparing base (4aff730) to head (f3f4e1f).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10684         +/-   ##
===================================================
+ Coverage   11.28308%   11.36855%   +0.08547%     
===================================================
  Files           3353        3354          +1     
  Lines         668062      668045         -17     
  Branches       74980       74981          +1     
===================================================
+ Hits           75378       75947        +569     
+ Misses        591433      590847        -586     
  Partials        1251        1251                 

Flag	Coverage Δ
Debug	11.36855% <0.00000%> (+0.08547%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.