improve generation performance

[jantimon]

Description

graphql-codegen-cli/src/generate-and-save.ts has more filesystem than neccessary:

1. Checking for existence before reading. (from the official nodejs docs):

Using fs.exists() to check for the existence of a file before calling fs.open(), fs.readFile() or fs.writeFile() is not recommended.

2. After reading the file from disk and generating the hash, the hash is not stored.
   So if the previousHash matches the currentHash the file will be read again from disk.

3. mkdirp is now built into node

This PR improves all three cases and in addition fixes a bug where input.cwd is not passed to mkdirp.

How Has This Been Tested?

All unit tests + tested on my machine - would love to get feedback from a windows user.

Test Environment:

• OS: MacOs 13
• @graphql-codegen/...:
• NodeJS: 16

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[changeset-bot]

🦋 Changeset detected

Latest commit: a27b71f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@graphql-codegen/cli	Patch
@graphql-cli/codegen	Patch

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[charlypoly]

@ardatan I put you in review to QA on Windows 👀 🪟

[saihaj]

https://github.com/dotansimha/graphql-code-generator/releases/tag/release-1669393783419