Fix resource type completion for JSON

[Ben-Wormald]

Issue #, if available: #450

Description of changes:

• Fix replacement range being set too high
• Keep object keys when completing values e.g. resource types
• Simplify JSON formatting function for future improvements

There is still some behaviour for JSON completions that isn't ideal but hopefully this is a first steo to improving it, cheers

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[satyakigh]

Hello, thank you for the PR! We will review this soon

[Zee2413]

Do we need to add AWSTemplateFormatVersion here?

[Ben-Wormald]

I didn't include it here originally as there's a snippet completion which completes the whole line with "AWSTemplateFormatVersion": "2010-09-09"

However it looks like both that snippet and an object placeholder snippet are suggested, I can take a look at that

[satyakigh]

Seems like the build is failing, I think this change potentially introduces some regressions which may or may not have been caught by the removed test(s)

1. filterText removed (JSON) — Editors send quoted prefixes like "Res" when cursor is inside a JSON string, without filterText, completions won't match

2. Resource attributes lose type formatting (JSON) — DependsOn, Metadata, CreationPolicy, UpdatePolicy, etc. are created by EntityFieldCompletionProvider with no data.type

3. Resource type textEdit range removed (YAML) — We set an explicit replacement range via textEdit when the user was partially typing a resource type. With the removal, since resource types contain ::, partial input like AWS::S3::B may get incorrectly replaced, producing AWS::S3::AWS::S3::Bucket

Would love to see some more unit tests around these edge cases