Be smart about newlines before/after extractions

[StephenWeatherford]

The new behavior is essentially that we try to match the newly-inserted declaration (whether it has blank lines before/after) with the existing declaration that it's being inserted after. For example:

var v1 = 1
var v2 = 2

var expression = v1 + v2   // << EXTRACT THIS
``
=>
```bicep
var v1 = 1
var v2 = 2
var newVariable = v1 + v2  // << NEW DECLARATION

var expression = newVariable
``
Since v2 had a newline after it but none before it, we do the same with newVariable.  If there were a blank line between v1 and v2, we'd insert a blank line before newVariable.
 ###### Microsoft Reviewers: [Open in CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/Azure/bicep/pull/15194)

[github-actions]

Test this change out locally with the following install scripts (Action run 11173740548)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 11173740548

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 11173740548"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 11173740548

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 11173740548"

[github-actions]

Dotnet Test Results

    72 files   -     24      72 suites   - 24   28m 23s ⏱️ - 18m 17s
11 310 tests +    16  11 310 ✅ +    16  0 💤 ±0  0 ❌ ±0 
26 397 runs   - 11 186  26 397 ✅  - 11 186  0 💤 ±0  0 ❌ ±0 

Results for commit 643f340. ± Comparison against base commit da3c2ce.

♻️ This comment has been updated with latest results.

[shenglol]