[WIP] Lowering string interpolation to calls to concat

[abonie]

Description

A draft PR to test on CI.

The idea is to lower string interpolation to a call to concat if interpolated string has at most 4 parts and all the parts are strings.

TODOs:

• More IL tests?
• Benchmark
• Filter out empty strings? E.g. $"{0}{1}" has technically 5 parts - an empty string, first interpolated expression, an empty string, second interpolated expression and another empty string
• Benchmark
• Make the code nicer

Fixes # (issue, if applicable)

Checklist

• Test cases added

• Performance benchmarks added in case of performance changes

• Release notes entry updated:

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Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/8.0.300.md	No release notes found or release notes format is not correct