Remove array/object allocs during Alt+Numpad composition, improve performance

[h3xds1nz]

Description

Removes unnecessary byte[] , char[] and StringBuilder alocations during post-input processing when the char is inputted via Alt+Numpad combination. This is not somewhat impactful allocation but it will allow for more optimizations in the future.

Time spent is cut by 2/5 which is more impactful in this case.

GetCurrentOEMCPEncoding method chain call

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	48.77 ns	0.674 ns	0.630 ns	0.0086	814 B	144 B
PR_EDIT	31.83 ns	0.292 ns	0.273 ns	0.0019	418 B	32 B

Customer Impact

Improved performance, decreased allocations.

Regression

No.

Testing

Local build, text input.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow