fix(backup): use Conditions instead of ListOfTags in BackupSelection

[emfrab]

Issue # (if applicable)

Closes #37771
Closes #18911

Reason for this change

BackupSelection generates a ListOfTags CloudFormation property instead of Conditions. This has two consequences:

1. Wrong logic: ListOfTags uses OR semantics — a resource matching any tag is selected. Conditions uses AND semantics — a resource must match all conditions. The AWS Console's "Tags - equal" filter uses Conditions, so tag-based selections created via CDK behave differently than equivalent console-created selections.
2. Limited operations: ListOfTags only supports StringEquals. Conditions supports StringEquals, StringLike, StringNotEquals, and StringNotLike.

Additionally, TagOperation had a placeholder DUMMY member instead of the three missing operations, and the resources array on BackupSelectionOptions mixes ARN resources with tag conditions in a way that implies per-ARN scoping that doesn't exist in the underlying API.

Description of changes

• selection.ts: Replaces listOfTags: ListOfTags with a conditions: Conditions block in the generated CloudFormation. Four per-operation arrays (stringEquals, stringLike, stringNotEquals, stringNotLike) accumulate conditions and are serialized using PascalCase keys (required because conditions is typed as any in the generated layer, bypassing CDK's camelCase→PascalCase transformation). Extracts addTagCondition() as a shared private method.
• selection.ts: Adds tagConditions?: TagCondition[] to BackupSelectionOptions. This is the preferred way to add tag-based filtering — it makes clear at the API level that conditions are selection-wide, not scoped to a single ARN.
• resource.ts: Adds STRING_LIKE, STRING_NOT_EQUALS, STRING_NOT_LIKE to TagOperation; removes DUMMY. Deprecates BackupResource.fromTag() in favor of tagConditions.

BackupResource.fromTag() continues to work unchanged for backwards compatibility.

Describe any new or updated permissions being added

None.

Description of how you validated changes

• Updated and created tests
• Compiled the modified code and tested it manually

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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