Revert storing Font glyphs in manually-allocated memory

[oxan]

Instead of replacing the std::vector with manually allocated memory, use ExternalRAMAllocator as an allocator for the std::vector.

This also reverts the graceful handling of allocation failure for the glyphs, but that didn't work correctly anyway: if glyph allocation failed and DisplayBuffer::print() was called, a null pointer (this->glyphs_[0]) was dereferenced in Font::match_next_glyph. While not ideal, I'd rather have abort() be called on the allocation failure, as that at least makes clear what's going wrong.

This partially reverts commit 62459a8 (PR #4485).

What does this implement/fix?

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040

Example entry for config.yaml:

# Example config.yaml

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.