Fix a bug parsing files with ! operator

[Pr0methean]

I have a Cfn template that uses ! as a type specifier before strings that contain newlines. For example:

            /etc/cfn/cfn-hup.conf:
              content:
                Fn::Join:
                - ''
                - - ! '[main]

'
                  - stack=
                  - Ref: AWS::StackId
                  - ! '

'
                  - region=
                  - Ref: AWS::Region
                  - ! '

'
              group: root
              mode: '000444'
              owner: root

That leads to errors like these:

Error: Resources.ArtifactEncryptionKey.Properties.KeyPolicy.Statement[0].Principal.AWS.Fn::Join[1][0]: unknown variant `!`, expected one of `Base64`, `Cidr`, `FindInMap`, `GetAtt`, `GetAZs`, `If`, `ImportValue`, `Join`, `Select`, `Split`, `Sub`, `Ref` at line 205 column 19

This PR fixes those errors by changing the return type of IntrinsicFunction::from_enum so that it can wrap the next token instead of an IntrinsicFunction, and adding a match case for "!" that does so.

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 #389 (2af15de) into main (8f9e75b) will decrease coverage by 0.0%.
The diff coverage is 42.9%.

Components	Coverage Δ
Parser	77.1% <42.9%> (-0.4%)	⬇️
Intermediate Representation	82.1% <ø> (ø)
Synthesizers	87.8% <ø> (ø)
Other	45.8% <ø> (ø)

@@           Coverage Diff           @@
##            main    #389     +/-   ##
=======================================
- Coverage   84.1%   84.0%   -0.0%     
=======================================
  Files         27      27             
  Lines       4752    4756      +4     
  Branches    4752    4756      +4     
=======================================
+ Hits        3995    3996      +1     
- Misses       559     562      +3     
  Partials     198     198             

Files	Coverage Δ
src/parser/resource/mod.rs	78.7% <100.0%> (ø)
src/parser/intrinsics/mod.rs	70.7% <33.3%> (-1.5%)	⬇️

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[TheRealAmazonKendra]

Thank you for your contribution. Please add a test case that covers this change and make sure the code is passing the linter.