tgc-revival: refactor compute instance flatten functions

[zli82016]

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit f384ea3:

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Repository	Diff Link	Changes
terraform-google-conversion	View Diff	2 files changed, 1090 insertions(+), 104 deletions(-)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit 0d56e17:

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Your PR generated the following diffs in downstream repositories:

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terraform-google-conversion	View Diff	2 files changed, 1090 insertions(+), 104 deletions(-)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit 048612f:

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Your PR generated the following diffs in downstream repositories:

Repository	Diff Link	Changes
terraform-google-conversion	View Diff	1 file changed, 594 insertions(+), 104 deletions(-)