performance: avoid file watchers

[justinmk3]

Problem

Toolkit has various file watchers for SAM template.yaml files, CDK, etc. These can negatively affect performance.

Solution

1. Introduce settings to limit the cost of Toolkit file watchers:
2. ✅ exclude files/directories specified by vscode search.exclude, files.exclude settings. https://github.com/aws/aws-toolkit-vscode/pull/3770
3. ✅ Change template.yaml detect to be on-demand instead of eager (omnipresent, filewatcher-driven)
   • When a template.yaml is needed but not found (such as "SAM run/debug", and "Sync SAM" command), mention this in the info message. (Related: #3211)
   • Implemented in #3931 + #3962

[justinmk3]

The "schema service" in particular can be a complete show-stopper if your workspace has many big projects (which... may contain... yaml files):

2023-03-27 19:46:16 [DEBUG]: schema service: handle yaml mapping: sam -> file:///projects/sam-installation/aws-sam-cli-src/tests/smoke/templates/sar/s3-uncompressor-template.yaml
2023-03-27 19:46:16 [DEBUG]: schema service: handle yaml mapping: sam -> file:///projects/sam-installation/aws-sam-cli-src/tests/smoke/templates/sar/alexa-skills-kit-color-expert-template.yaml
2023-03-27 19:46:16 [DEBUG]: schema service: handle yaml mapping: sam -> file:///projects/sam-installation/aws-sam-cli-src/tests/smoke/templates/sar/SecretsManagerRedshiftRotationSingleUser-template.yaml
2023-03-27 19:46:17 [DEBUG]: schema service: handle yaml mapping: sam -> file:///projects/sam-installation/aws-sam-cli-src/tests/smoke/templates/sar/magic-8-ball-template.yaml
2023-03-27 19:46:17 [DEBUG]: schema service: handle yaml mapping: sam -> file:///projects/sam-installation/aws-sam-cli-src/tests/smoke/templates/sar/SecretsManagerMongoDBRotationSingleUser-template.yaml
2023-03-27 19:46:17 [DEBUG]: schema service: handle yaml mapping: sam -> file:///projects/sam-installation/aws-sam-cli-src/tests/smoke/templates/sar/AmazonConnectSalesforceLambda-template.yaml
<100s more...>

• The above workspace has 40739 files and AWS Toolkit stalls 5+ minutes at startup (doesn't block the rest of the IDE but does block the Toolkit itself!).
• Easier to reproduce on a vm with a slow(ish) filesystem, such as a CodeCatalyst devenv.

Exacerbated by https://github.com/aws/aws-toolkit-vscode/issues/3259 ?

This thing even drills into node_modules :( (Update: https://github.com/aws/aws-toolkit-vscode/pull/3440 )

2023-03-31 08:49:16 [DEBUG]: schema service: handle yaml mapping: [removed] -> file:///Volumes/workplace/aws-toolkit-vscode/node_modules/buffer/.travis.yml
2023-03-31 08:49:16 [DEBUG]: schema service: handle yaml mapping: [removed] -> file:///Volumes/workplace/aws-toolkit-vscode/node_modules/buffer/bin/zuul-es6.yml
...

[justinmk3]

Item 3 in the above list was implemented in #3931 + #3962.

File watchers are still not fully avoided though. That's tracked elsewhere, so closing this issue.