[STEP-2562] Parse xcodebuild_options into typed options

[lpusok]

SplitAdditionalOptions splits the xcodebuild_options input with POSIX shell rules
(go-shellquote's Split, which the steps have always used on it), and
ParseAdditionalOptions reads the arguments as xcodebuild does:

• every argument is a switch, a flag with a value (-flag value, -flag:value), a user
  default (-Key=value), a build setting (NAME=value, split at the first "="), or a build
  action; there is no dictionary of xcodebuild flags, so flags of a newer Xcode work;
• a flag takes the next argument as its value unless that is a flag, a NAME=value or an
  action; a short hint list of flags whose values can look like one (-destination
  platform=..., -scheme test, -derivedDataPath build) always takes it;
• what fits no form is kept verbatim as Unknown with the reason (an empty argument, a flag
  quoted together with its value, a bare word from an unquoted value with spaces);
• parsing round-trips: Args() gives back the arguments it was given.

Options.Filter selects by kind, for steps that forward part of the options, such as
xcode-archive's build settings and package flags for -showBuildSettings.

The builders still append the options verbatim; nothing here changes a command line.

🤖 Generated with Claude Code

[Copilot]

🟡 Changes recommended

Unknown-option diagnostics are inaccessible to consumers of the public parsing API.

1 open finding

• Expose diagnostic details for unknown parsed arguments · New

What changed in this PR

Adds typed parsing and filtering for shell-split xcodebuild_options while preserving argument round-tripping.

Changes:

• Classifies switches, value options, defaults, settings, actions, and unknown arguments.
• Adds filtering, keying, rendering, and comprehensive parser tests.
• Adds go-shellquote for POSIX-compatible splitting.

File	Description
xcodecommand/​xcodebuild.go	Defines recognized build actions.
xcodecommand/​options.go	Implements splitting, parsing, classification, and filtering.
xcodecommand/​options_test.go	Tests parser behavior and round-tripping.
go.mod	Adds the shell-splitting dependency.
go.sum	Records dependency checksums.

🧠 Review effort: Balanced

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