Fix TaskParameterTaskItem serialization perf

[ccastanedaucf]

Fixes

Fixes several hotspots I found while profiling RAR service serialization.

Changes Made

• Fix effectively doubling the work in the write direction, where TaskParameterTaskItem is created to wrap an existing TaskItem, but then of its metadata is parsed one again right before serialization
• Use MSBuildNameIgnoreCaseComparer.Default (by moving it into Framework`
• Avoid additional call to retrieve value when enumerating dictionary returned by ITaskItem2.CloneCustomMetadataEscaped(). If this is a Utilities.TaskItem coming back from a task, doing an accessor check is non-negligible overhead due to CopyOnWriteDictionary.
• SImplify translation logic. Prefer unidirectional ITranslator APIs over manually checking each direction or reimplementing methods, and let TaskParameterTaskItem handle its own serialization.

A bunch of small improvements but they add up. Since the out of proc TaskHost is the only piece currently using this, here's some profiles off my RAR service builds.

TaskParameterTaskItem.CopyMetadataTo()

This is often hit by ReferenceTable.SetItemMetadata in RAR. This fix here was to use IMetadataContainer.ImportMetadata() bulk set, since ImmutableDictionary performs better when operations are batched.

Before:

After:

Double ITaskItem parsing

Essentially when in the write direction the old code would construct a TaskParameterTaskItem, but later cast it to ITaskItem and parse everything out again. You can see this here where CloneCustomMetadataEscaped() is hit even though by this point we've already extracted the external TaskItem to our own instance.

Before:

After:

ItemSpec unescaped value caching

Added a simple cache around ItemSpec property accesses. Might be worth porting this into ProjectItemInstance.TaskItem and Utilities.TaskItem since this is hit very often.

I'm showing this one as a backtrace to show where this is hit.

Before:

After:

This actually appears to just no-op most of the time since most of the time is spent in String.IndexOf():

[ccastanedaucf]

lol probably broke something while pulling this out of my RAR branch, will check UT failures later today

[ccastanedaucf]

Updated with profile traces now that I've fully isolated it from other perf stuff. Tests passing so should be good to go 👍

[ccastanedaucf]

Tbh not sure why IMetadataContainer is conditioned out of the taskhost beside the extra source file (compiles fine with it), but I've kept it here anyways.

[ccastanedaucf]

Based on that profile showing SetMetadata("OrignalItemSpec") adding still time under here, maybe worth joining it into the IEnumerable to avoid immediately copying a new ImmutableDictionary right after this block - haven't checked to see if IEnumerable.Concat() or spread operator works efficiently or ends up allocating a collection. Otherwise a local function + yield return would work