split customize_diff, schema_version, and migrate_state from resource definition files

[NickElliot]

Removes all but one resource_definition file and adds new custom_code attributes for mentioning custom_diff and migrate_state functions directly. To preserve the current functionality of schema_version when included .yaml schemas, a new attribute boolean has been added called "state_upgraders" for when that version compatibility feature needs to be used with the schema.

Work is required to remove a blocker on hashicorp/terraform-provider-google#11339 for resources that have existing customize_diff functions.

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read Write release notes before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 290 files changed, 882 insertions(+), 22 deletions(-))
Terraform Beta: Diff ( 351 files changed, 1066 insertions(+), 23 deletions(-))
TF Conversion: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2815
Passed tests 2511
Skipped tests: 301
Affected tests: 3

Action taken

Found 3 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccFolderIamPolicy_basic|TestAccComputeNetworkEndpoints_networkEndpointsBasic|TestAccComputeFirewallPolicyRule_multipleRules

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccFolderIamPolicy_basic[Debug log]
TestAccComputeNetworkEndpoints_networkEndpointsBasic[Debug log]

Tests failed during RECORDING mode:
TestAccComputeFirewallPolicyRule_multipleRules[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 26 files changed, 81 insertions(+), 22 deletions(-))
Terraform Beta: Diff ( 27 files changed, 85 insertions(+), 23 deletions(-))
TF Conversion: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2816
Passed tests 2513
Skipped tests: 301
Affected tests: 2

Action taken

Found 2 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccComputeNetworkEndpoints_networkEndpointsBasic|TestAccComputeFirewallPolicyRule_multipleRules

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccComputeNetworkEndpoints_networkEndpointsBasic[Debug log]

Tests failed during RECORDING mode:
TestAccComputeFirewallPolicyRule_multipleRules[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test

[c2thorn]

new attributes make sense to me and the resulting diffs look good. LGTM

[NickElliot]

Going to move the migrate_state and custom_diff blocks out of custom_code at Riley's suggestion

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 26 files changed, 81 insertions(+), 22 deletions(-))
Terraform Beta: Diff ( 27 files changed, 85 insertions(+), 23 deletions(-))
TF Conversion: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[NickElliot]

Same diffs produced, will merge soon.

[modular-magician]

Tests analytics

Total tests: 2819
Passed tests 2516
Skipped tests: 301
Affected tests: 2

Action taken

Found 2 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccComputeNetworkEndpoints_networkEndpointsBasic|TestAccComputeFirewallPolicyRule_multipleRules

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccComputeNetworkEndpoints_networkEndpointsBasic[Debug log]

Tests failed during RECORDING mode:
TestAccComputeFirewallPolicyRule_multipleRules[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test