Refactor parsing in bevy_reflect path module

[nicopap]

Objective

• Follow up to Refactor path module of bevy_reflect #8887
• The parsing code in bevy_reflect/src/path/mod.rs could also do with some cleanup

Solution

• Create the parse.rs module, move all parsing code to this module
• The parsing errors also now keep track of the whole parsed string, and are much more fine-grained

Detailed changes

• Move PathParser to parse.rs submodule
• Rename token_to_access to access_following (yep, goes from 132 lines to 16)
• Move parsing tests into the parse.rs file

[nicopap]

I found out that parsing in "ascii mode" is much better in terms of performance. And there is no reason to not do it (apart from maintainability). What I will do is remove the comment wrt alternative impl and open a performance PR with all the unsafe.

[nicopap]

This is the optimized version I came up with:

https://gist.github.com/nicopap/9a1c04bf549914036ea5cc5d6e23269b

[MrGVSV]

This is the optimized version I came up with:

https://gist.github.com/nicopap/9a1c04bf549914036ea5cc5d6e23269b

Are you planning to add this optimized version in this PR or opening a followup PR?

[nicopap]

Are you planning to add this optimized version in this PR or opening a followup PR?

follow up PR

[MrGVSV]

Looks great! Just two nits and then some other non-blocking comments.

[MrGVSV]

Nit: Not blocking, but while we're here could we add some tests for the other kinds of errors?