chore(amplify-category-custom): error if resource dir does not exist

[josefaidt]

Description of changes

• adds an error if a custom resource directory does not exist
• adds tests for new error
• adds tests for missing TypeScript executable

Issue #, if available

Description of how you validated changes

ran tests with yarn test

Checklist

• [x] PR description included
• [x] yarn test passes
• [x] Tests are changed or added
• [ ] Relevant documentation is changed or added (and PR referenced)
• [ ] New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• [ ] Pull request labels are added

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #12333 (6338546) into dev (984c0f8) will decrease coverage by 2.18%. The diff coverage is 58.75%.

:exclamation: Current head 6338546 differs from pull request most recent head a229b95. Consider uploading reports for the commit a229b95 to get more accurate results

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@@            Coverage Diff             @@
##              dev   #12333      +/-   ##
==========================================
- Coverage   49.45%   47.27%   -2.18%     
==========================================
  Files         692      839     +147     
  Lines       33424    38212    +4788     
  Branches     6840     7772     +932     
==========================================
+ Hits        16529    18065    +1536     
- Misses      15370    18510    +3140     
- Partials     1525     1637     +112     

Impacted Files	Coverage Δ
...mplify-appsync-simulator/src/resolvers/function.ts	15.38% <ø> (ø)
...s/amplify-appsync-simulator/src/type-definition.ts	100.00% <ø> (ø)
...sync-simulator/src/velocity/util/dynamodb-utils.ts	6.55% <0.00%> (ø)
...y-appsync-simulator/src/velocity/util/map-utils.ts	10.00% <ø> (ø)
...tor/src/velocity/util/transform/dynamodb-filter.ts	4.93% <0.00%> (ø)
...appsync-simulator/src/velocity/value-mapper/map.ts	86.88% <ø> (ø)
...ackages/amplify-category-auth/src/commands/auth.ts	0.00% <0.00%> (ø)
...ges/amplify-category-auth/src/commands/auth/add.ts	0.00% <ø> (ø)
...es/amplify-category-auth/src/commands/auth/help.ts	0.00% <0.00%> (ø)
.../amplify-category-auth/src/commands/auth/import.ts	0.00% <0.00%> (ø)
... and 92 more

... and 477 files with indirect coverage changes

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[sobolk]

@josefaidt can you merge dev and make tests pass ?