[Repo Assist] perf: avoid O(n²) allocations in ILMethodDefs; use lazy caches in TargetTypeDefinition member lookups (#497)

🤖 *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:
```fsharp
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:
```fsharp
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`).




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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

src/ProvidedTypes.fs

@@ -2881,12 +2881,16 @@ module internal AssemblyReader =
     type ILMethodDefs(larr: Lazy<ILMethodDef[]>) =
 
         let lmap = lazy (
-            let m = Dictionary()
+            // Use ResizeArray during construction to avoid O(n^2) allocations when
+            // building per-name buckets for overloaded methods.
+            let tmp = Dictionary<string, ResizeArray<ILMethodDef>>()
             for y in larr.Force() do
                 let key = y.Name
-                match m.TryGetValue key with
-                | true, lmpak -> m.[key] <- Array.append [| y |] lmpak
-                | false, _ -> m.[key] <- [| y |]
+                match tmp.TryGetValue key with
+                | true, ra -> ra.Add y
+                | false, _ -> tmp.[key] <- ResizeArray [y]
+            let m = Dictionary<string, ILMethodDef[]>(tmp.Count)
+            for kvp in tmp do m.[kvp.Key] <- kvp.Value.ToArray()
             m)
         let getmap() = lmap.Value
 
@@ -8058,19 +8062,13 @@ namespace ProviderImplementation.ProvidedTypes
             md |> Option.map (txILMethodDef this) |> Option.toObj
 
         override this.GetField(name, _bindingFlags) =
-            inp.Fields.Entries
-            |> Array.tryPick (fun p -> if p.Name = name then Some (txILFieldDef this p) else None)
-            |> Option.toObj
+            fieldDefs.Force() |> Array.tryFind (fun f -> f.Name = name) |> Option.toObj
 
         override this.GetPropertyImpl(name, _bindingFlags, _binder, _returnType, _types, _modifiers) =
-            inp.Properties.Entries
-            |> Array.tryPick (fun p -> if p.Name = name then Some (txILPropertyDef this p) else None)
-            |> Option.toObj
+            propDefs.Force() |> Array.tryFind (fun p -> p.Name = name) |> Option.toObj
 
         override this.GetEvent(name, _bindingFlags) =
-            inp.Events.Entries
-            |> Array.tryPick (fun ev -> if ev.Name = name then Some (txILEventDef this ev) else None)
-            |> Option.toObj
+            eventDefs.Force() |> Array.tryFind (fun ev -> ev.Name = name) |> Option.toObj
 
         override this.GetNestedType(name, _bindingFlags) =
             inp.NestedTypes.TryFindByName(UNone, name) |> Option.map (asm.TxILTypeDef (Some (this :> Type))) |> Option.toObj