OpenAPI Common Parameters

[reuvenharrison]

Improve handling of Common Parameters

Common Parameters definition in OpenAPI spec:
Common Parameters for All Methods of a Path
Parameters shared by all operations of a path can be defined on the path level instead of the operation level. Path-level parameters are inherited by all operations of that path. A typical use case are the GET/PUT/PATCH/DELETE operations that manipulate a resource accessed via a path parameter.

This PR improves the results of: diff, breaking changes, and changelog with regards to common parameters.
Prior to the PR, common parameters were considered separately from the operation parameters.
After this PR, common parameters will be moved from the path and combined with operation parameters before running the diff.
As a result, the existing logic for operation parameters (diff, breaking changes, changelog etc.) will also be applied to common parameters.

New --flatten-params can be used with diff, breaking, changelog, delta and summary commands:

oasdiff changelog data/path-params/params_in_path.yaml data/path-params/params_in_op.yaml --flatten-params

For conformance, I'm also renaming the flatten flag as flatten-allof.
The old flatten flag will still be supported but will be hidden.

[codecov-commenter]

Codecov Report

Attention: 48 lines in your changes are missing coverage. Please review.

Comparison is base (a2470e3) 83.75% compared to head (5283b5c) 83.96%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
internal/diff_flags.go	63.63%	16 Missing ⚠️
delta/endpoints.go	79.31%	4 Missing and 2 partials ⚠️
load/spec_info.go	76.92%	4 Missing and 2 partials ⚠️
internal/cmd_flags.go	88.57%	3 Missing and 1 partial ⚠️
delta/parameters.go	90.62%	2 Missing and 1 partial ⚠️
delta/schema.go	57.14%	2 Missing and 1 partial ⚠️
internal/delta.go	88.88%	2 Missing and 1 partial ⚠️
load/option.go	86.95%	2 Missing and 1 partial ⚠️
internal/changelog_flags.go	95.45%	2 Missing ⚠️
delta/delta.go	95.00%	1 Missing ⚠️
... and 1 more

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #479      +/-   ##
==========================================
+ Coverage   83.75%   83.96%   +0.21%     
==========================================
  Files         217      228      +11     
  Lines       12593    12899     +306     
==========================================
+ Hits        10547    10831     +284     
- Misses       1668     1688      +20     
- Partials      378      380       +2     

Flag	Coverage Δ
unittests	83.96% <89.16%> (+0.21%)	⬆️

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