Update PostCSS to v8.4.49 and improve code readability

[Vhivi]

This pull request includes several changes to improve code readability and update dependencies. The most important changes include adding braces to single-line if statements, refactoring PostCSS plugin definitions, and updating the postcss dependency version.

Code readability improvements:

• Added braces to single-line if statements in lib/compileTemplate.ts, lib/parse.ts, lib/styleProcessors/index.ts, lib/templateCompilerModules/assetUrl.ts, and lib/templateCompilerModules/srcset.ts to improve readability. [1] [2] [3] [4] [5] [6]

PostCSS plugin refactoring:

• Refactored PostCSS plugin definitions in lib/stylePlugins/scoped.ts and lib/stylePlugins/trim.ts to use the new plugin API format. [1] [2] [3]

Dependency updates:

• Updated postcss dependency to version 8.4.49 in package.json and moved it to peerDependencies. [1] [2]