[wasm] Reduce allocation when options are passed to fetch

[maraf]

We can skip creating a list of options and than converting to array, because we can calculate in advance number of options being used in the HTTP call.

Note: The same doesn't apply for headers, because we don't know number of values for each header.

[ghost]

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Issue Details

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We can skip creating a list of options and than converting to array, because we can calculate in advance number of options being used in the HTTP call.

Note: The same doesn't apply for headers, because we don't know number of values for each header.

Author:	maraf
Assignees:	maraf
Labels:	arch-wasm, area-System.Net.Http
Milestone:	-

[maraf]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[maraf]

/backport to release/7.0-rc1

[github-actions]

Started backporting to release/7.0-rc1: https://github.com/dotnet/runtime/actions/runs/2888490989