[Desktop] Show warning when user tries to close code words modal

[btlechowski]

In sync 1 closing code words modal during creation process did not matter because the sync chain was created anyway.

This is changed in sync 2 where closing the code words modal will cancel the creation process and therefor create new code words. User may not expect that new code words will be generated.

We show warning when user tries to reload the sync page when code words modal is shown. We should do the same when user cancels the process by pressing Escape or clicking x on code words modal

Steps to Reproduce

1. Clean install
2. Open brave://settings/braveSync/setup
3. Click Start a new sync chain
4. Click Computer
5. Copy code words
6. Click x located in the top right corner OR press Escape

Actual result:

Sync chain creation process is canceled without warning

Expected result:

Warning is shown

Reproduces how often:

100% repro rate

Brave version (brave://version info)

Brave	1.12.94 Chromium: 84.0.4147.89 (Official Build) dev (64-bit)
Revision	19abfe7bcba9318a0b2a6bc6634a67fc834aa592-refs/branch-heads/4147@{#852}
OS	Ubuntu 18.04 LTS

Brave	1.13.36 Chromium: 84.0.4147.89 (Official Build) nightly (64-bit)
Revision	19abfe7bcba9318a0b2a6bc6634a67fc834aa592-refs/branch-heads/4147@{#852}
OS	Ubuntu 18.04 LTS

cc @brave/legacy_qa @jsecretan @rebron @darkdh @AlexeyBarabash @yrliou @petemill

[GeetaSarvadnya]

Reproduced on Windows 10 x64 - 1.12.108

[AlexeyBarabash]

I can reproduce this .