Optimize FigureLength struct conversion to string, reduce allocations

[h3xds1nz]

Description

Optimizes conversion of FigureLength to string. Simplifies Can* methods, adds some documentation.

• The benchmark is done with Redefine FigureLength as readonly struct to prevent defensive copies #9887 which allows for better perf navigating through the methods.

Simple ToString conversion

Method	figureLength	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	999	102.3501 ns	2.0471 ns	3.0640 ns	0.0048	4,171 B	80 B
PR__EDIT	999	76.9590 ns	1.3950 ns	1.2367 ns	0.0029	957 B	48 B

yield return new FigureLength(999.0, FigureUnitType.Column);

Customer Impact

Improved performance, decreased allocations.

Regression

No.

Testing

Local build, conversion tests.

Risk

Low; do note that #9887 should be taken first imho.

Microsoft Reviewers: Open in CodeFlow