Add IS_BROWSER constant to GenericNode

[lukechu10]

This fixes the ugly hack of using

if TypeId::of::<G>() == TypeId::of::<DomNode>() { ... }

and replaces it with

if G::IS_BROWSER { ... }

[jquesada2016]

@lukechu10 Since you mentioned wanting to support other platforms in the future, wouldn't it be wiser to change the IS_BROWSER constant to something like PLATFORM_NAME or PLATFORM with an enum which can include a variant for custom for user provided renderers? This does solve the ugly hack, but doesn't help when targeting other runtimes, such as NativeScript, React Native, etc.

[lukechu10]

@lukechu10 Since you mentioned wanting to support other platforms in the future, wouldn't it be wiser to change the IS_BROWSER constant to something like PLATFORM_NAME or PLATFORM with an enum which can include a variant for custom for user provided renderers? This does solve the ugly hack, but doesn't help when targeting other runtimes, such as NativeScript, React Native, etc.

Only web apps need to be isomorphic, meaning that they should render with both DomNode and SsrNode. For other platforms, there will only ever be one single backend and so this will not be used. In fact, now that I think about it, maybe the constant should go on the new Html trait (that is only implemented for DomNode and SsrNode) instead of GenericNode.

[codecov-commenter]

Codecov Report

Merging #274 (2f51b18) into master (59765a1) will not change coverage.
The diff coverage is 66.66%.

@@           Coverage Diff           @@
##           master     #274   +/-   ##
=======================================
  Coverage   74.93%   74.93%           
=======================================
  Files          33       33           
  Lines        4800     4800           
=======================================
  Hits         3597     3597           
  Misses       1203     1203           

Impacted Files	Coverage Δ
packages/sycamore-macro/src/template/component.rs	64.00% <ø> (ø)
packages/sycamore/src/generic_node/dom_node.rs	0.00% <ø> (ø)
packages/sycamore/src/generic_node/ssr_node.rs	76.45% <ø> (ø)
packages/sycamore/src/lib.rs	100.00% <ø> (ø)
packages/sycamore/src/portal.rs	0.00% <ø> (ø)
website/src/main.rs	0.98% <0.00%> (ø)
packages/sycamore-macro/src/component/mod.rs	73.86% <100.00%> (ø)

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