[Repo Assist] perf: avoid O(n²) allocations in ILMethodDefs; use lazy caches in TargetTypeDefinition member lookups

[github-actions]

🤖 This is an automated PR from Repo Assist.

Summary

Two complementary performance improvements to TargetTypeDefinition and the internal ILMethodDefs name-index.

1. O(1)-per-entry method-name index construction (ILMethodDefs.lmap)

Before: the lazy name→methods dictionary was built by prepending each new entry to an existing array:

m.[key] <- Array.append [| y |] lmpak   // O(n) per insertion

For a type with N methods sharing a name, this allocates arrays of sizes 1, 2, 3 … N — O(N²) total elements. The BCL contains types (e.g. String, Convert) with dozens of overloads per name, making this measurable.

After: a ResizeArray accumulator collects entries per name in O(1) each, then a single ToArray() call per bucket produces the final arrays — O(N) total elements.

2. Lazy-cache reuse in GetField, GetPropertyImpl, GetEvent

Before: each call to GetField/GetPropertyImpl/GetEvent scanned the raw ILFieldDef/ILPropertyDef/ILEventDef arrays and called the txIL* factory to create a brand-new wrapper object:

inp.Fields.Entries |> Array.tryPick (fun p -> if p.Name = name then Some (txILFieldDef this p) else None)

This created a new allocation on every call even when fieldDefs/propDefs/eventDefs lazy arrays were already fully computed (e.g. after a preceding GetFields(bindingFlags) call).

After: the methods call Force() on the already-computed lazy arrays and filter by name. When the caches are warm (the common case during compilation) zero new wrappers are allocated, and callers get consistent object identity across GetFields/GetField pairs.

Test Status

✅ 126/126 tests pass (dotnet test tests/FSharp.TypeProviders.SDK.Tests.fsproj).

Generated by 🌈 Repo Assist, see workflow run. Learn more.

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@e1ecf341a90b7bc2021e77c58685d7e269e20b99