Fix Cadence 1.0 migration of dictionary values when using atree inlined data

[fxamacker]

Closes #3288

This PR fixes MigrateNestedValue() for dictionary values.

Previously, MigrateNestedValue() migrates dictionary by using readonly iterator and migrating values in place.

This PR migrates keys first using read-only iterator and then migrates values using mutable iterator.

More details at the test/reproducer:

• Add reproducer as test for Cadence 1.0 migration issue #3288 #3314

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[turbolent]

Great fix!

As discussed in the review meeting, splitting up the migration into a pass migrating the keys using read-only iteration, and another pass migrating the values using mutable iteration, makes sense 👍

I only realized this after the call but: To have the atree-register inlining branch not drift too much, let's apply the refactor to master, even if it is not needed.

[turbolent]

@fxamacker I'm working on porting this to master. After that we can improve it a bit more (TODOs we discussed), update the atree register inlining branch, and then add the tests with #3314

[fxamacker]

@turbolent Thanks for approving and code review of this PR yesterday!

In addition to passing all tests in PR #3314, I also verified this morning that it resolves "slab not found error" using input file tn-a47a2d3a3b7e9133-inlined.payloads you extracted last week while investigating #3288.

[turbolent]

@fxamacker Awesome! Thank you for checking this, it's great to see the fix works as expected 👌

[turbolent]

@fxamacker Ported this to master in #3318, and added the improvements we discussed yesterday. PTAL 🙏