fix(all): Fn::ImportValue fails during deserialization if it contains nested intrinsic function

[colifran]

This PR fixes a bug that causes failures if a CloudFormation template contains Fn::ImportValue with a nested intrinsic function as a value.

At a high-level, this bug was a result of the IntrinsicFunction enum representing ImportValue as a string. As a result, nested Fn::ImportValue with a nested intrinsic function will fail to synthesize with the following error message:

Migrate failed for `<stack name>`: stack generation failed due to error '<Resource Path>.Fn::ImportValue: invalid type: map, expected a string at ...'

stack generation failed due to error '<Resource Path>.Fn::ImportValue: invalid type: map, expected a string at ...'

The fix for this bug is to update the IntrinsicFunction enum to represent ImportValue as a ResourceType.

Fixes #29014

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Merging #581 (3d6f74f) into main (65fe906) will increase coverage by 0.2%.
The diff coverage is 95.5%.

Additional details and impacted files

Components	Coverage Δ
Parser	76.2% <ø> (ø)
Intermediate Representation	79.4% <66.7%> (+0.6%)	⬆️
Synthesizers	87.3% <100.0%> (+0.1%)	⬆️
Other	34.3% <ø> (ø)

@@           Coverage Diff           @@
##            main    #581     +/-   ##
=======================================
+ Coverage   80.8%   81.0%   +0.2%     
=======================================
  Files         27      27             
  Lines       5075    5092     +17     
  Branches    5075    5092     +17     
=======================================
+ Hits        4101    4123     +22     
+ Misses       773     767      -6     
- Partials     201     202      +1     

Files	Coverage Δ
src/parser/intrinsics/mod.rs	68.1% <ø> (ø)
src/synthesizer/csharp/mod.rs	85.1% <100.0%> (+0.1%)	⬆️
src/synthesizer/golang/mod.rs	85.0% <100.0%> (+0.1%)	⬆️
src/synthesizer/java/mod.rs	87.8% <100.0%> (+0.1%)	⬆️
src/synthesizer/python/mod.rs	89.1% <100.0%> (+0.1%)	⬆️
src/synthesizer/typescript/mod.rs	89.6% <100.0%> (+<0.1%)	⬆️
src/ir/resources/mod.rs	78.3% <66.7%> (+1.1%)	⬆️

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