fix(cli): handle Cordova plugins without iOS source files

[OS-ruimoreiramendes]

• Fix getPluginPlatform to return undefined instead of [] when a plugin has no <platform> tags
• Skip Package.swift generation for Cordova plugins with <platform name="ios"> but no source files
• Skip adding those plugins to the generated CapApp-SPM/Package.swift

Reference: https://outsystemsrd.atlassian.net/browse/RMET-5159

Tests
Validated with three dummy plugins:
test-plugin-no-platform: no <platform> tags -> correctly skipped as incompatible
test-plugin-no-sources: <platform name="ios"> with only entries -> sync completes, config still processed
test-plugin-with-sources: <platform name="ios"> with source files -> continues to work normally

[jcesarmobile]

if the plugin gets skipped as incompatible, then the copying of the plugin's .js files also gets skipped, that's why getPluginPlatform is returning [] instead of undefined, so even if there is no native files, the .js files still get copied.
So getPluginPlatform shouldn't be changed to return undefined.

[OS-ruimoreiramendes]

if the plugin gets skipped as incompatible, then the copying of the plugin's .js files also gets skipped, that's why getPluginPlatform is returning [] instead of undefined, so even if there is no native files, the .js files still get copied. So getPluginPlatform shouldn't be changed to return undefined.

confirmed your point. With undefined, plugins without a <platform> tag were marked as Incompatible and their .js files were not copied. With [] it works correctly.
Reverted.

[alexgerardojacinto]

Minor: I think the PR title should be fix(cli):...